ICU-64232.0.1.tar.gz

[apple/icu.git] / icuSources / common / unicode / unistr.h

diff --git a/icuSources/common/unicode/unistr.h b/icuSources/common/unicode/unistr.h
index 3827458bfb9df9e3b67b240937200d883b1f7071..55739ac2425fd1840a6d7dffc8c31bc189300adc 100644 (file)
--- a/icuSources/common/unicode/unistr.h
+++ b/icuSources/common/unicode/unistr.h
@@ -1,6 +1,8 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html

 /*
 **********************************************************************
 /*
 **********************************************************************

-*   Copyright (C) 1998-2004, International Business Machines
+*   Copyright (C) 1998-2016, International Business Machines

 *   Corporation and others.  All Rights Reserved.
 **********************************************************************
 *
 *   Corporation and others.  All Rights Reserved.
 **********************************************************************
 *


@@ -21,32 +23,65 @@
 #ifndef UNISTR_H
 #define UNISTR_H
 
 #ifndef UNISTR_H
 #define UNISTR_H
 

+/**
+ * \file
+ * \brief C++ API: Unicode String
+ */
+
+#include <cstddef>
+#include "unicode/utypes.h"
+#include "unicode/char16ptr.h"

 #include "unicode/rep.h"
 #include "unicode/rep.h"

+#include "unicode/std_string.h"
+#include "unicode/stringpiece.h"
+#include "unicode/bytestream.h"

 
 struct UConverter;          // unicode/ucnv.h
 
 struct UConverter;          // unicode/ucnv.h

-class  StringThreadTest;

 
 

-#ifndef U_COMPARE_CODE_POINT_ORDER
-/* see also ustring.h and unorm.h */
+#ifndef USTRING_H

 /**
 /**

- * Option bit for u_strCaseCompare, u_strcasecmp, unorm_compare, etc:
- * Compare strings in code point order instead of code unit order.
- * @stable ICU 2.2
+ * \ingroup ustring_ustrlen

  */
  */

-#define U_COMPARE_CODE_POINT_ORDER  0x8000
-#endif
-
-#ifndef USTRING_H
-/* see ustring.h */

 U_STABLE int32_t U_EXPORT2
 u_strlen(const UChar *s);
 #endif
 
 U_STABLE int32_t U_EXPORT2
 u_strlen(const UChar *s);
 #endif
 

+#if U_SHOW_CPLUSPLUS_API
+U_NAMESPACE_BEGIN
+
+#if !UCONFIG_NO_BREAK_ITERATION
+class BreakIterator;        // unicode/brkiter.h
+#endif
+class Edits;
+
+U_NAMESPACE_END
+#endif // U_SHOW_CPLUSPLUS_API
+
+#if U_SHOW_CPLUSPLUS_API
+// Not #ifndef U_HIDE_INTERNAL_API because UnicodeString needs the UStringCaseMapper.
+/**
+ * Internal string case mapping function type.
+ * All error checking must be done.
+ * src and dest must not overlap.
+ * @internal
+ */
+typedef int32_t U_CALLCONV
+UStringCaseMapper(int32_t caseLocale, uint32_t options,
+#if !UCONFIG_NO_BREAK_ITERATION
+                  icu::BreakIterator *iter,
+#endif
+                  char16_t *dest, int32_t destCapacity,
+                  const char16_t *src, int32_t srcLength,
+                  icu::Edits *edits,
+                  UErrorCode &errorCode);
+#endif // U_SHOW_CPLUSPLUS_API
+
+#if U_SHOW_CPLUSPLUS_API

 U_NAMESPACE_BEGIN
 
 class Locale;               // unicode/locid.h
 class StringCharacterIterator;
 U_NAMESPACE_BEGIN
 
 class Locale;               // unicode/locid.h
 class StringCharacterIterator;

-class BreakIterator;        // unicode/brkiter.h
+class UnicodeStringAppendable;  // unicode/appendable.h

 
 /* The <iostream> include has been moved to unicode/ustream.h */
 
 
 /* The <iostream> include has been moved to unicode/ustream.h */
 


@@ -58,33 +93,31 @@ class BreakIterator;        // unicode/brkiter.h
  * therefore recommended over ones taking a charset name string
  * (where the empty string "" indicates invariant-character conversion).
  *
  * therefore recommended over ones taking a charset name string
  * (where the empty string "" indicates invariant-character conversion).
  *

- * @draft ICU 3.2
+ * @stable ICU 3.2

  */
  */

-#define US_INV UnicodeString::kInvariant
+#define US_INV icu::UnicodeString::kInvariant

 
 /**
  * Unicode String literals in C++.
 
 /**
  * Unicode String literals in C++.

- * Dependent on the platform properties, different UnicodeString
- * constructors should be used to create a UnicodeString object from
- * a string literal.
- * The macros are defined for maximum performance.
+ *
+ * Note: these macros are not recommended for new code.
+ * Prior to the availability of C++11 and u"unicode string literals",
+ * these macros were provided for portability and efficiency when
+ * initializing UnicodeStrings from literals.
+ *

  * They work only for strings that contain "invariant characters", i.e.,
  * only latin letters, digits, and some punctuation.
  * See utypes.h for details.
  *
  * The string parameter must be a C string literal.
  * The length of the string, not including the terminating
  * They work only for strings that contain "invariant characters", i.e.,
  * only latin letters, digits, and some punctuation.
  * See utypes.h for details.
  *
  * The string parameter must be a C string literal.
  * The length of the string, not including the terminating

- * <code>NUL</code>, must be specified as a constant.
- * The U_STRING_DECL macro should be invoked exactly once for one
- * such string variable before it is used.
+ * `NUL`, must be specified as a constant.

  * @stable ICU 2.0
  */
  * @stable ICU 2.0
  */

-#if U_SIZEOF_WCHAR_T==U_SIZEOF_UCHAR && U_CHARSET_FAMILY==U_ASCII_FAMILY
-#   define UNICODE_STRING(cs, _length) UnicodeString(TRUE, (const UChar *)L ## cs, _length)
-#elif U_SIZEOF_UCHAR==1 && U_CHARSET_FAMILY==U_ASCII_FAMILY
-#   define UNICODE_STRING(cs, _length) UnicodeString(TRUE, (const UChar *)cs, _length)
+#if !U_CHAR16_IS_TYPEDEF
+# define UNICODE_STRING(cs, _length) icu::UnicodeString(TRUE, u ## cs, _length)

 #else
 #else

-#   define UNICODE_STRING(cs, _length) UnicodeString(cs, _length, US_INV)
+# define UNICODE_STRING(cs, _length) icu::UnicodeString(TRUE, (const char16_t*)u ## cs, _length)

 #endif
 
 /**
 #endif
 
 /**


@@ -100,48 +133,128 @@ class BreakIterator;        // unicode/brkiter.h
  * The string parameter must be a C string literal.
  * @stable ICU 2.0
  */
  * The string parameter must be a C string literal.
  * @stable ICU 2.0
  */

-#if U_SIZEOF_WCHAR_T==U_SIZEOF_UCHAR && U_CHARSET_FAMILY==U_ASCII_FAMILY
-#   define UNICODE_STRING_SIMPLE(cs) UnicodeString(TRUE, (const UChar *)L ## cs, -1)
-#elif U_SIZEOF_UCHAR==1 && U_CHARSET_FAMILY==U_ASCII_FAMILY
-#   define UNICODE_STRING_SIMPLE(cs) UnicodeString(TRUE, (const UChar *)cs, -1)
-#else
-#   define UNICODE_STRING_SIMPLE(cs) UnicodeString(cs, -1, US_INV)
+#define UNICODE_STRING_SIMPLE(cs) UNICODE_STRING(cs, -1)
+
+/**
+ * \def UNISTR_FROM_CHAR_EXPLICIT
+ * This can be defined to be empty or "explicit".
+ * If explicit, then the UnicodeString(char16_t) and UnicodeString(UChar32)
+ * constructors are marked as explicit, preventing their inadvertent use.
+ * @stable ICU 49
+ */
+#ifndef UNISTR_FROM_CHAR_EXPLICIT
+# if defined(U_COMBINED_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION) || defined(U_I18N_IMPLEMENTATION) || defined(U_IO_IMPLEMENTATION)
+    // Auto-"explicit" in ICU library code.
+#   define UNISTR_FROM_CHAR_EXPLICIT explicit
+# else
+    // Empty by default for source code compatibility.
+#   define UNISTR_FROM_CHAR_EXPLICIT
+# endif
+#endif
+
+/**
+ * \def UNISTR_FROM_STRING_EXPLICIT
+ * This can be defined to be empty or "explicit".
+ * If explicit, then the UnicodeString(const char *) and UnicodeString(const char16_t *)
+ * constructors are marked as explicit, preventing their inadvertent use.
+ *
+ * In particular, this helps prevent accidentally depending on ICU conversion code
+ * by passing a string literal into an API with a const UnicodeString & parameter.
+ * @stable ICU 49
+ */
+#ifndef UNISTR_FROM_STRING_EXPLICIT
+# if defined(U_COMBINED_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION) || defined(U_I18N_IMPLEMENTATION) || defined(U_IO_IMPLEMENTATION)
+    // Auto-"explicit" in ICU library code.
+#   define UNISTR_FROM_STRING_EXPLICIT explicit
+# else
+    // Empty by default for source code compatibility.
+#   define UNISTR_FROM_STRING_EXPLICIT
+# endif
+#endif
+
+/**
+ * \def UNISTR_OBJECT_SIZE
+ * Desired sizeof(UnicodeString) in bytes.
+ * It should be a multiple of sizeof(pointer) to avoid unusable space for padding.
+ * The object size may want to be a multiple of 16 bytes,
+ * which is a common granularity for heap allocation.
+ *
+ * Any space inside the object beyond sizeof(vtable pointer) + 2
+ * is available for storing short strings inside the object.
+ * The bigger the object, the longer a string that can be stored inside the object,
+ * without additional heap allocation.
+ *
+ * Depending on a platform's pointer size, pointer alignment requirements,
+ * and struct padding, the compiler will usually round up sizeof(UnicodeString)
+ * to 4 * sizeof(pointer) (or 3 * sizeof(pointer) for P128 data models),
+ * to hold the fields for heap-allocated strings.
+ * Such a minimum size also ensures that the object is easily large enough
+ * to hold at least 2 char16_ts, for one supplementary code point (U16_MAX_LENGTH).
+ *
+ * sizeof(UnicodeString) >= 48 should work for all known platforms.
+ *
+ * For example, on a 64-bit machine where sizeof(vtable pointer) is 8,
+ * sizeof(UnicodeString) = 64 would leave space for
+ * (64 - sizeof(vtable pointer) - 2) / U_SIZEOF_UCHAR = (64 - 8 - 2) / 2 = 27
+ * char16_ts stored inside the object.
+ *
+ * The minimum object size on a 64-bit machine would be
+ * 4 * sizeof(pointer) = 4 * 8 = 32 bytes,
+ * and the internal buffer would hold up to 11 char16_ts in that case.
+ *
+ * @see U16_MAX_LENGTH
+ * @stable ICU 56
+ */
+#ifndef UNISTR_OBJECT_SIZE
+# define UNISTR_OBJECT_SIZE 64

 #endif
 
 /**
  * UnicodeString is a string class that stores Unicode characters directly and provides
 #endif
 
 /**
  * UnicodeString is a string class that stores Unicode characters directly and provides

- * similar functionality as the Java String and StringBuffer classes.
+ * similar functionality as the Java String and StringBuffer/StringBuilder classes.

  * It is a concrete implementation of the abstract class Replaceable (for transliteration).
  *
  * It is a concrete implementation of the abstract class Replaceable (for transliteration).
  *

+ * A UnicodeString may also "alias" an external array of characters
+ * (that is, point to it, rather than own the array)
+ * whose lifetime must then at least match the lifetime of the aliasing object.
+ * This aliasing may be preserved when returning a UnicodeString by value,
+ * depending on the compiler and the function implementation,
+ * via Return Value Optimization (RVO) or the move assignment operator.
+ * (However, the copy assignment operator does not preserve aliasing.)
+ * For details see the description of storage models at the end of the class API docs
+ * and in the User Guide chapter linked from there.
+ *

  * The UnicodeString class is not suitable for subclassing.
  *
  * The UnicodeString class is not suitable for subclassing.
  *

- * <p>For an overview of Unicode strings in C and C++ see the
- * <a href="http://oss.software.ibm.com/icu/userguide/strings.html">User Guide Strings chapter</a>.</p>
+ * For an overview of Unicode strings in C and C++ see the
+ * [User Guide Strings chapter](http://userguide.icu-project.org/strings#TOC-Strings-in-C-C-).

  *
  *

- * <p>In ICU, a Unicode string consists of 16-bit Unicode <em>code units</em>.
- * A Unicode character may be stored with either
- * one code unit &#8212; which is the most common case &#8212; or with a matched pair of
- * special code units ("surrogates").
- * The data type for code units is UChar.<br>
- * For single-character handling, a Unicode character code <em>point</em> is a value
- * in the range 0..0x10ffff. ICU uses the UChar32 type for code points.</p>
+ * In ICU, a Unicode string consists of 16-bit Unicode *code units*.
+ * A Unicode character may be stored with either one code unit
+ * (the most common case) or with a matched pair of special code units
+ * ("surrogates"). The data type for code units is char16_t.
+ * For single-character handling, a Unicode character code *point* is a value
+ * in the range 0..0x10ffff. ICU uses the UChar32 type for code points.

  *
  *

- * <p>Indexes and offsets into and lengths of strings always count code units, not code points.
+ * Indexes and offsets into and lengths of strings always count code units, not code points.

  * This is the same as with multi-byte char* strings in traditional string handling.
  * Operations on partial strings typically do not test for code point boundaries.
  * If necessary, the user needs to take care of such boundaries by testing for the code unit
  * values or by using functions like
  * UnicodeString::getChar32Start() and UnicodeString::getChar32Limit()
  * This is the same as with multi-byte char* strings in traditional string handling.
  * Operations on partial strings typically do not test for code point boundaries.
  * If necessary, the user needs to take care of such boundaries by testing for the code unit
  * values or by using functions like
  * UnicodeString::getChar32Start() and UnicodeString::getChar32Limit()

- * (or, in C, the equivalent macros U16_SET_CP_START() and U16_SET_CP_LIMIT(), see utf.h).</p>
+ * (or, in C, the equivalent macros U16_SET_CP_START() and U16_SET_CP_LIMIT(), see utf.h).

  *
  * UnicodeString methods are more lenient with regard to input parameter values
  * than other ICU APIs. In particular:
  * - If indexes are out of bounds for a UnicodeString object
  *
  * UnicodeString methods are more lenient with regard to input parameter values
  * than other ICU APIs. In particular:
  * - If indexes are out of bounds for a UnicodeString object

- *   (<0 or >length()) then they are "pinned" to the nearest boundary.
- * - If primitive string pointer values (e.g., const UChar * or char *)
+ *   (< 0 or > length()) then they are "pinned" to the nearest boundary.
+ * - If the buffer passed to an insert/append/replace operation is owned by the
+ *   target object, e.g., calling str.append(str), an extra copy may take place
+ *   to ensure safety.
+ * - If primitive string pointer values (e.g., const char16_t * or char *)

  *   for input strings are NULL, then those input string parameters are treated
  *   as if they pointed to an empty string.
  *   for input strings are NULL, then those input string parameters are treated
  *   as if they pointed to an empty string.

- *   However, this is <em>not</em> the case for char * parameters for charset names
+ *   However, this is *not* the case for char * parameters for charset names

  *   or other IDs.
  * - Most UnicodeString methods do not take a UErrorCode parameter because
  *   there are usually very few opportunities for failure other than a shortage
  *   or other IDs.
  * - Most UnicodeString methods do not take a UErrorCode parameter because
  *   there are usually very few opportunities for failure other than a shortage


@@ -165,14 +278,14 @@ class BreakIterator;        // unicode/brkiter.h
  * This includes the const UnicodeString & parameters for
  * copy construction, assignment, and cloning.
  *
  * This includes the const UnicodeString & parameters for
  * copy construction, assignment, and cloning.
  *

- * <p>UnicodeString uses several storage methods.
+ * UnicodeString uses several storage methods.

  * String contents can be stored inside the UnicodeString object itself,
  * in an allocated and shared buffer, or in an outside buffer that is "aliased".
  * Most of this is done transparently, but careful aliasing in particular provides
  * significant performance improvements.
  * Also, the internal buffer is accessible via special functions.
  * For details see the
  * String contents can be stored inside the UnicodeString object itself,
  * in an allocated and shared buffer, or in an outside buffer that is "aliased".
  * Most of this is done transparently, but careful aliasing in particular provides
  * significant performance improvements.
  * Also, the internal buffer is accessible via special functions.
  * For details see the

- * <a href="http://oss.software.ibm.com/icu/userguide/strings.html">User Guide Strings chapter</a>.</p>
+ * [User Guide Strings chapter](http://userguide.icu-project.org/strings#TOC-Maximizing-Performance-with-the-UnicodeString-Storage-Model).

  *
  * @see utf.h
  * @see CharacterIterator
  *
  * @see utf.h
  * @see CharacterIterator


@@ -188,12 +301,12 @@ public:
    * Use the macro US_INV instead of the full qualification for this value.
    *
    * @see US_INV
    * Use the macro US_INV instead of the full qualification for this value.
    *
    * @see US_INV

-   * @draft ICU 3.2
+   * @stable ICU 3.2

    */
   enum EInvariant {
     /**
      * @see EInvariant
    */
   enum EInvariant {
     /**
      * @see EInvariant

-     * @draft ICU 3.2
+     * @stable ICU 3.2

      */
     kInvariant
   };
      */
     kInvariant
   };


@@ -207,7 +320,7 @@ public:
   /**
    * Equality operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
   /**
    * Equality operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.

-   * @return TRUE if <TT>text</TT> contains the same characters as this one,
+   * @return TRUE if `text` contains the same characters as this one,

    * FALSE otherwise.
    * @stable ICU 2.0
    */
    * FALSE otherwise.
    * @stable ICU 2.0
    */


@@ -216,7 +329,7 @@ public:
   /**
    * Inequality operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
   /**
    * Inequality operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.

-   * @return FALSE if <TT>text</TT> contains the same characters as this one,
+   * @return FALSE if `text` contains the same characters as this one,

    * TRUE otherwise.
    * @stable ICU 2.0
    */
    * TRUE otherwise.
    * @stable ICU 2.0
    */


@@ -226,7 +339,7 @@ public:
    * Greater than operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise
    * Greater than operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise

-   * greater than the characters in <code>text</code>, FALSE otherwise
+   * greater than the characters in `text`, FALSE otherwise

    * @stable ICU 2.0
    */
   inline UBool operator> (const UnicodeString& text) const;
    * @stable ICU 2.0
    */
   inline UBool operator> (const UnicodeString& text) const;


@@ -235,7 +348,7 @@ public:
    * Less than operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise
    * Less than operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise

-   * less than the characters in <code>text</code>, FALSE otherwise
+   * less than the characters in `text`, FALSE otherwise

    * @stable ICU 2.0
    */
   inline UBool operator< (const UnicodeString& text) const;
    * @stable ICU 2.0
    */
   inline UBool operator< (const UnicodeString& text) const;


@@ -244,7 +357,7 @@ public:
    * Greater than or equal operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise
    * Greater than or equal operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise

-   * greater than or equal to the characters in <code>text</code>, FALSE otherwise
+   * greater than or equal to the characters in `text`, FALSE otherwise

    * @stable ICU 2.0
    */
   inline UBool operator>= (const UnicodeString& text) const;
    * @stable ICU 2.0
    */
   inline UBool operator>= (const UnicodeString& text) const;


@@ -253,36 +366,37 @@ public:
    * Less than or equal operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise
    * Less than or equal operator. Performs only bitwise comparison.
    * @param text The UnicodeString to compare to this one.
    * @return TRUE if the characters in this are bitwise

-   * less than or equal to the characters in <code>text</code>, FALSE otherwise
+   * less than or equal to the characters in `text`, FALSE otherwise

    * @stable ICU 2.0
    */
   inline UBool operator<= (const UnicodeString& text) const;
 
   /**
    * Compare the characters bitwise in this UnicodeString to
    * @stable ICU 2.0
    */
   inline UBool operator<= (const UnicodeString& text) const;
 
   /**
    * Compare the characters bitwise in this UnicodeString to

-   * the characters in <code>text</code>.
+   * the characters in `text`.

    * @param text The UnicodeString to compare to this one.
    * @return The result of bitwise character comparison: 0 if this
    * @param text The UnicodeString to compare to this one.
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>text</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>text</code>, +1 if the
+   * contains the same characters as `text`, -1 if the characters in
+   * this are bitwise less than the characters in `text`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>text</code>.
+   * in `text`.

    * @stable ICU 2.0
    */
   inline int8_t compare(const UnicodeString& text) const;
 
   /**
    * Compare the characters bitwise in the range
    * @stable ICU 2.0
    */
   inline int8_t compare(const UnicodeString& text) const;
 
   /**
    * Compare the characters bitwise in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the characters
-   * in <TT>text</TT>
+   * [`start`, `start + length`) with the characters
+   * in the **entire string** `text`.
+   * (The parameters "start" and "length" are not applied to the other text "text".)

    * @param start the offset at which the compare operation begins
    * @param length the number of characters of text to compare.
    * @param text the other text to be compared against this string.
    * @return The result of bitwise character comparison: 0 if this
    * @param start the offset at which the compare operation begins
    * @param length the number of characters of text to compare.
    * @param text the other text to be compared against this string.
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>text</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>text</code>, +1 if the
+   * contains the same characters as `text`, -1 if the characters in
+   * this are bitwise less than the characters in `text`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>text</code>.
+   * in `text`.

    * @stable ICU 2.0
    */
   inline int8_t compare(int32_t start,
    * @stable ICU 2.0
    */
   inline int8_t compare(int32_t start,


@@ -291,19 +405,19 @@ public:
 
   /**
    * Compare the characters bitwise in the range
 
   /**
    * Compare the characters bitwise in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the characters
-   * in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
+   * [`start`, `start + length`) with the characters
+   * in `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`).

    * @param start the offset at which the compare operation begins
    * @param length the number of characters in this to compare.
    * @param srcText the text to be compared
    * @param start the offset at which the compare operation begins
    * @param length the number of characters in this to compare.
    * @param srcText the text to be compared

-   * @param srcStart the offset into <TT>srcText</TT> to start comparison
-   * @param srcLength the number of characters in <TT>src</TT> to compare
+   * @param srcStart the offset into `srcText` to start comparison
+   * @param srcLength the number of characters in `src` to compare

    * @return The result of bitwise character comparison: 0 if this
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>srcText</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>srcText</code>, +1 if the
+   * contains the same characters as `srcText`, -1 if the characters in
+   * this are bitwise less than the characters in `srcText`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>srcText</code>.
+   * in `srcText`.

    * @stable ICU 2.0
    */
    inline int8_t compare(int32_t start,
    * @stable ICU 2.0
    */
    inline int8_t compare(int32_t start,


@@ -314,75 +428,75 @@ public:
 
   /**
    * Compare the characters bitwise in this UnicodeString with the first
 
   /**
    * Compare the characters bitwise in this UnicodeString with the first

-   * <TT>srcLength</TT> characters in <TT>srcChars</TT>.
+   * `srcLength` characters in `srcChars`.

    * @param srcChars The characters to compare to this UnicodeString.
    * @param srcChars The characters to compare to this UnicodeString.

-   * @param srcLength the number of characters in <TT>srcChars</TT> to compare
+   * @param srcLength the number of characters in `srcChars` to compare

    * @return The result of bitwise character comparison: 0 if this
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>srcChars</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>srcChars</code>, +1 if the
+   * contains the same characters as `srcChars`, -1 if the characters in
+   * this are bitwise less than the characters in `srcChars`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>srcChars</code>.
+   * in `srcChars`.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int8_t compare(const UChar *srcChars,
+  inline int8_t compare(ConstChar16Ptr srcChars,

          int32_t srcLength) const;
 
   /**
    * Compare the characters bitwise in the range
          int32_t srcLength) const;
 
   /**
    * Compare the characters bitwise in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the first
-   * <TT>length</TT> characters in <TT>srcChars</TT>
+   * [`start`, `start + length`) with the first
+   * `length` characters in `srcChars`

    * @param start the offset at which the compare operation begins
    * @param length the number of characters to compare.
    * @param srcChars the characters to be compared
    * @return The result of bitwise character comparison: 0 if this
    * @param start the offset at which the compare operation begins
    * @param length the number of characters to compare.
    * @param srcChars the characters to be compared
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>srcChars</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>srcChars</code>, +1 if the
+   * contains the same characters as `srcChars`, -1 if the characters in
+   * this are bitwise less than the characters in `srcChars`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>srcChars</code>.
+   * in `srcChars`.

    * @stable ICU 2.0
    */
   inline int8_t compare(int32_t start,
          int32_t length,
    * @stable ICU 2.0
    */
   inline int8_t compare(int32_t start,
          int32_t length,

-         const UChar *srcChars) const;
+         const char16_t *srcChars) const;

 
   /**
    * Compare the characters bitwise in the range
 
   /**
    * Compare the characters bitwise in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the characters
-   * in <TT>srcChars</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
+   * [`start`, `start + length`) with the characters
+   * in `srcChars` in the range
+   * [`srcStart`, `srcStart + srcLength`).

    * @param start the offset at which the compare operation begins
    * @param length the number of characters in this to compare
    * @param srcChars the characters to be compared
    * @param start the offset at which the compare operation begins
    * @param length the number of characters in this to compare
    * @param srcChars the characters to be compared

-   * @param srcStart the offset into <TT>srcChars</TT> to start comparison
-   * @param srcLength the number of characters in <TT>srcChars</TT> to compare
+   * @param srcStart the offset into `srcChars` to start comparison
+   * @param srcLength the number of characters in `srcChars` to compare

    * @return The result of bitwise character comparison: 0 if this
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>srcChars</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>srcChars</code>, +1 if the
+   * contains the same characters as `srcChars`, -1 if the characters in
+   * this are bitwise less than the characters in `srcChars`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>srcChars</code>.
+   * in `srcChars`.

    * @stable ICU 2.0
    */
   inline int8_t compare(int32_t start,
          int32_t length,
    * @stable ICU 2.0
    */
   inline int8_t compare(int32_t start,
          int32_t length,

-         const UChar *srcChars,
+         const char16_t *srcChars,

          int32_t srcStart,
          int32_t srcLength) const;
 
   /**
    * Compare the characters bitwise in the range
          int32_t srcStart,
          int32_t srcLength) const;
 
   /**
    * Compare the characters bitwise in the range

-   * [<TT>start</TT>, <TT>limit</TT>) with the characters
-   * in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcLimit</TT>).
+   * [`start`, `limit`) with the characters
+   * in `srcText` in the range
+   * [`srcStart`, `srcLimit`).

    * @param start the offset at which the compare operation begins
    * @param limit the offset immediately following the compare operation
    * @param srcText the text to be compared
    * @param start the offset at which the compare operation begins
    * @param limit the offset immediately following the compare operation
    * @param srcText the text to be compared

-   * @param srcStart the offset into <TT>srcText</TT> to start comparison
-   * @param srcLimit the offset into <TT>srcText</TT> to limit comparison
+   * @param srcStart the offset into `srcText` to start comparison
+   * @param srcLimit the offset into `srcText` to limit comparison

    * @return The result of bitwise character comparison: 0 if this
    * @return The result of bitwise character comparison: 0 if this

-   * contains the same characters as <code>srcText</code>, -1 if the characters in
-   * this are bitwise less than the characters in <code>srcText</code>, +1 if the
+   * contains the same characters as `srcText`, -1 if the characters in
+   * this are bitwise less than the characters in `srcText`, +1 if the

    * characters in this are bitwise greater than the characters
    * characters in this are bitwise greater than the characters

-   * in <code>srcText</code>.
+   * in `srcText`.

    * @stable ICU 2.0
    */
   inline int8_t compareBetween(int32_t start,
    * @stable ICU 2.0
    */
   inline int8_t compareBetween(int32_t start,


@@ -393,7 +507,7 @@ public:
 
   /**
    * Compare two Unicode strings in code point order.
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -412,7 +526,7 @@ public:
 
   /**
    * Compare two Unicode strings in code point order.
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -435,7 +549,7 @@ public:
 
   /**
    * Compare two Unicode strings in code point order.
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -462,7 +576,7 @@ public:
 
   /**
    * Compare two Unicode strings in code point order.
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -478,12 +592,12 @@ public:
    * in code point order
    * @stable ICU 2.0
    */
    * in code point order
    * @stable ICU 2.0
    */

-  inline int8_t compareCodePointOrder(const UChar *srcChars,
+  inline int8_t compareCodePointOrder(ConstChar16Ptr srcChars,

                                       int32_t srcLength) const;
 
   /**
    * Compare two Unicode strings in code point order.
                                       int32_t srcLength) const;
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -502,11 +616,11 @@ public:
    */
   inline int8_t compareCodePointOrder(int32_t start,
                                       int32_t length,
    */
   inline int8_t compareCodePointOrder(int32_t start,
                                       int32_t length,

-                                      const UChar *srcChars) const;
+                                      const char16_t *srcChars) const;

 
   /**
    * Compare two Unicode strings in code point order.
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -527,13 +641,13 @@ public:
    */
   inline int8_t compareCodePointOrder(int32_t start,
                                       int32_t length,
    */
   inline int8_t compareCodePointOrder(int32_t start,
                                       int32_t length,

-                                      const UChar *srcChars,
+                                      const char16_t *srcChars,

                                       int32_t srcStart,
                                       int32_t srcLength) const;
 
   /**
    * Compare two Unicode strings in code point order.
                                       int32_t srcStart,
                                       int32_t srcLength) const;
 
   /**
    * Compare two Unicode strings in code point order.

-   * This is different in UTF-16 from how compare(), operator==, startsWith() etc. work
+   * The result may be different from the results of compare(), operator<, etc.

    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are
    * if supplementary characters are present:
    *
    * In UTF-16, supplementary characters (with code points U+10000 and above) are


@@ -651,7 +765,7 @@ public:
    * @return A negative, zero, or positive integer indicating the comparison result.
    * @stable ICU 2.0
    */
    * @return A negative, zero, or positive integer indicating the comparison result.
    * @stable ICU 2.0
    */

-  inline int8_t caseCompare(const UChar *srcChars,
+  inline int8_t caseCompare(ConstChar16Ptr srcChars,

          int32_t srcLength,
          uint32_t options) const;
 
          int32_t srcLength,
          uint32_t options) const;
 


@@ -677,7 +791,7 @@ public:
    */
   inline int8_t caseCompare(int32_t start,
          int32_t length,
    */
   inline int8_t caseCompare(int32_t start,
          int32_t length,

-         const UChar *srcChars,
+         const char16_t *srcChars,

          uint32_t options) const;
 
   /**
          uint32_t options) const;
 
   /**


@@ -704,7 +818,7 @@ public:
    */
   inline int8_t caseCompare(int32_t start,
          int32_t length,
    */
   inline int8_t caseCompare(int32_t start,
          int32_t length,

-         const UChar *srcChars,
+         const char16_t *srcChars,

          int32_t srcStart,
          int32_t srcLength,
          uint32_t options) const;
          int32_t srcStart,
          int32_t srcLength,
          uint32_t options) const;


@@ -739,21 +853,21 @@ public:
             uint32_t options) const;
 
   /**
             uint32_t options) const;
 
   /**

-   * Determine if this starts with the characters in <TT>text</TT>
+   * Determine if this starts with the characters in `text`

    * @param text The text to match.
    * @param text The text to match.

-   * @return TRUE if this starts with the characters in <TT>text</TT>,
+   * @return TRUE if this starts with the characters in `text`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
   inline UBool startsWith(const UnicodeString& text) const;
 
   /**
    * FALSE otherwise
    * @stable ICU 2.0
    */
   inline UBool startsWith(const UnicodeString& text) const;
 
   /**

-   * Determine if this starts with the characters in <TT>srcText</TT>
-   * in the range [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
+   * Determine if this starts with the characters in `srcText`
+   * in the range [`srcStart`, `srcStart + srcLength`).

    * @param srcText The text to match.
    * @param srcText The text to match.

-   * @param srcStart the offset into <TT>srcText</TT> to start matching
-   * @param srcLength the number of characters in <TT>srcText</TT> to match
-   * @return TRUE if this starts with the characters in <TT>text</TT>,
+   * @param srcStart the offset into `srcText` to start matching
+   * @param srcLength the number of characters in `srcText` to match
+   * @return TRUE if this starts with the characters in `text`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
    * FALSE otherwise
    * @stable ICU 2.0
    */


@@ -762,45 +876,45 @@ public:
             int32_t srcLength) const;
 
   /**
             int32_t srcLength) const;
 
   /**

-   * Determine if this starts with the characters in <TT>srcChars</TT>
+   * Determine if this starts with the characters in `srcChars`

    * @param srcChars The characters to match.
    * @param srcChars The characters to match.

-   * @param srcLength the number of characters in <TT>srcChars</TT>
-   * @return TRUE if this starts with the characters in <TT>srcChars</TT>,
+   * @param srcLength the number of characters in `srcChars`
+   * @return TRUE if this starts with the characters in `srcChars`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
    * FALSE otherwise
    * @stable ICU 2.0
    */

-  inline UBool startsWith(const UChar *srcChars,
+  inline UBool startsWith(ConstChar16Ptr srcChars,

             int32_t srcLength) const;
 
   /**
             int32_t srcLength) const;
 
   /**

-   * Determine if this ends with the characters in <TT>srcChars</TT>
-   * in the range  [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
+   * Determine if this ends with the characters in `srcChars`
+   * in the range  [`srcStart`, `srcStart + srcLength`).

    * @param srcChars The characters to match.
    * @param srcChars The characters to match.

-   * @param srcStart the offset into <TT>srcText</TT> to start matching
-   * @param srcLength the number of characters in <TT>srcChars</TT> to match
-   * @return TRUE if this ends with the characters in <TT>srcChars</TT>, FALSE otherwise
+   * @param srcStart the offset into `srcText` to start matching
+   * @param srcLength the number of characters in `srcChars` to match
+   * @return TRUE if this ends with the characters in `srcChars`, FALSE otherwise

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline UBool startsWith(const UChar *srcChars,
+  inline UBool startsWith(const char16_t *srcChars,

             int32_t srcStart,
             int32_t srcLength) const;
 
   /**
             int32_t srcStart,
             int32_t srcLength) const;
 
   /**

-   * Determine if this ends with the characters in <TT>text</TT>
+   * Determine if this ends with the characters in `text`

    * @param text The text to match.
    * @param text The text to match.

-   * @return TRUE if this ends with the characters in <TT>text</TT>,
+   * @return TRUE if this ends with the characters in `text`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
   inline UBool endsWith(const UnicodeString& text) const;
 
   /**
    * FALSE otherwise
    * @stable ICU 2.0
    */
   inline UBool endsWith(const UnicodeString& text) const;
 
   /**

-   * Determine if this ends with the characters in <TT>srcText</TT>
-   * in the range [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
+   * Determine if this ends with the characters in `srcText`
+   * in the range [`srcStart`, `srcStart + srcLength`).

    * @param srcText The text to match.
    * @param srcText The text to match.

-   * @param srcStart the offset into <TT>srcText</TT> to start matching
-   * @param srcLength the number of characters in <TT>srcText</TT> to match
-   * @return TRUE if this ends with the characters in <TT>text</TT>,
+   * @param srcStart the offset into `srcText` to start matching
+   * @param srcLength the number of characters in `srcText` to match
+   * @return TRUE if this ends with the characters in `text`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
    * FALSE otherwise
    * @stable ICU 2.0
    */


@@ -809,27 +923,27 @@ public:
           int32_t srcLength) const;
 
   /**
           int32_t srcLength) const;
 
   /**

-   * Determine if this ends with the characters in <TT>srcChars</TT>
+   * Determine if this ends with the characters in `srcChars`

    * @param srcChars The characters to match.
    * @param srcChars The characters to match.

-   * @param srcLength the number of characters in <TT>srcChars</TT>
-   * @return TRUE if this ends with the characters in <TT>srcChars</TT>,
+   * @param srcLength the number of characters in `srcChars`
+   * @return TRUE if this ends with the characters in `srcChars`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
    * FALSE otherwise
    * @stable ICU 2.0
    */

-  inline UBool endsWith(const UChar *srcChars,
+  inline UBool endsWith(ConstChar16Ptr srcChars,

           int32_t srcLength) const;
 
   /**
           int32_t srcLength) const;
 
   /**

-   * Determine if this ends with the characters in <TT>srcChars</TT>
-   * in the range  [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
+   * Determine if this ends with the characters in `srcChars`
+   * in the range  [`srcStart`, `srcStart + srcLength`).

    * @param srcChars The characters to match.
    * @param srcChars The characters to match.

-   * @param srcStart the offset into <TT>srcText</TT> to start matching
-   * @param srcLength the number of characters in <TT>srcChars</TT> to match
-   * @return TRUE if this ends with the characters in <TT>srcChars</TT>,
+   * @param srcStart the offset into `srcText` to start matching
+   * @param srcLength the number of characters in `srcChars` to match
+   * @return TRUE if this ends with the characters in `srcChars`,

    * FALSE otherwise
    * @stable ICU 2.0
    */
    * FALSE otherwise
    * @stable ICU 2.0
    */

-  inline UBool endsWith(const UChar *srcChars,
+  inline UBool endsWith(const char16_t *srcChars,

           int32_t srcStart,
           int32_t srcLength) const;
 
           int32_t srcStart,
           int32_t srcLength) const;
 


@@ -837,21 +951,21 @@ public:
   /* Searching - bitwise only */
 
   /**
   /* Searching - bitwise only */
 
   /**

-   * Locate in this the first occurrence of the characters in <TT>text</TT>,
+   * Locate in this the first occurrence of the characters in `text`,

    * using bitwise comparison.
    * @param text The text to search for.
    * using bitwise comparison.
    * @param text The text to search for.

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
   inline int32_t indexOf(const UnicodeString& text) const;
 
   /**
    * or -1 if not found.
    * @stable ICU 2.0
    */
   inline int32_t indexOf(const UnicodeString& text) const;
 
   /**

-   * Locate in this the first occurrence of the characters in <TT>text</TT>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the first occurrence of the characters in `text`
+   * starting at offset `start`, using bitwise comparison.

    * @param text The text to search for.
    * @param start The offset at which searching will start.
    * @param text The text to search for.
    * @param start The offset at which searching will start.

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */


@@ -860,12 +974,12 @@ public:
 
   /**
    * Locate in this the first occurrence in the range
 
   /**
    * Locate in this the first occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>text</TT>, using bitwise comparison.
+   * [`start`, `start + length`) of the characters
+   * in `text`, using bitwise comparison.

    * @param text The text to search for.
    * @param start The offset at which searching will start.
    * @param length The number of characters to search
    * @param text The text to search for.
    * @param start The offset at which searching will start.
    * @param length The number of characters to search

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */


@@ -875,17 +989,17 @@ public:
 
   /**
    * Locate in this the first occurrence in the range
 
   /**
    * Locate in this the first occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   *  in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>),
+   * [`start`, `start + length`) of the characters
+   *  in `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`),

    * using bitwise comparison.
    * @param srcText The text to search for.
    * using bitwise comparison.
    * @param srcText The text to search for.

-   * @param srcStart the offset into <TT>srcText</TT> at which
+   * @param srcStart the offset into `srcText` at which

    * to start matching
    * to start matching

-   * @param srcLength the number of characters in <TT>srcText</TT> to match
+   * @param srcLength the number of characters in `srcText` to match

    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */


@@ -897,123 +1011,123 @@ public:
 
   /**
    * Locate in this the first occurrence of the characters in
 
   /**
    * Locate in this the first occurrence of the characters in

-   * <TT>srcChars</TT>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * `srcChars`
+   * starting at offset `start`, using bitwise comparison.

    * @param srcChars The text to search for.
    * @param srcChars The text to search for.

-   * @param srcLength the number of characters in <TT>srcChars</TT> to match
+   * @param srcLength the number of characters in `srcChars` to match

    * @param start the offset into this at which to start matching
    * @param start the offset into this at which to start matching

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */

-  inline int32_t indexOf(const UChar *srcChars,
+  inline int32_t indexOf(const char16_t *srcChars,

               int32_t srcLength,
               int32_t start) const;
 
   /**
    * Locate in this the first occurrence in the range
               int32_t srcLength,
               int32_t start) const;
 
   /**
    * Locate in this the first occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>srcChars</TT>, using bitwise comparison.
+   * [`start`, `start + length`) of the characters
+   * in `srcChars`, using bitwise comparison.

    * @param srcChars The text to search for.
    * @param srcChars The text to search for.

-   * @param srcLength the number of characters in <TT>srcChars</TT>
+   * @param srcLength the number of characters in `srcChars`

    * @param start The offset at which searching will start.
    * @param length The number of characters to search
    * @param start The offset at which searching will start.
    * @param length The number of characters to search

-   * @return The offset into this of the start of <TT>srcChars</TT>,
+   * @return The offset into this of the start of `srcChars`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */

-  inline int32_t indexOf(const UChar *srcChars,
+  inline int32_t indexOf(ConstChar16Ptr srcChars,

               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**
    * Locate in this the first occurrence in the range
               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**
    * Locate in this the first occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>srcChars</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>),
+   * [`start`, `start + length`) of the characters
+   * in `srcChars` in the range
+   * [`srcStart`, `srcStart + srcLength`),

    * using bitwise comparison.
    * @param srcChars The text to search for.
    * using bitwise comparison.
    * @param srcChars The text to search for.

-   * @param srcStart the offset into <TT>srcChars</TT> at which
+   * @param srcStart the offset into `srcChars` at which

    * to start matching
    * to start matching

-   * @param srcLength the number of characters in <TT>srcChars</TT> to match
+   * @param srcLength the number of characters in `srcChars` to match

    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */

-  int32_t indexOf(const UChar *srcChars,
+  int32_t indexOf(const char16_t *srcChars,

               int32_t srcStart,
               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**
               int32_t srcStart,
               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**

-   * Locate in this the first occurrence of the BMP code point <code>c</code>,
+   * Locate in this the first occurrence of the BMP code point `c`,

    * using bitwise comparison.
    * @param c The code unit to search for.
    * using bitwise comparison.
    * @param c The code unit to search for.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int32_t indexOf(UChar c) const;
+  inline int32_t indexOf(char16_t c) const;

 
   /**
 
   /**

-   * Locate in this the first occurrence of the code point <TT>c</TT>,
+   * Locate in this the first occurrence of the code point `c`,

    * using bitwise comparison.
    *
    * @param c The code point to search for.
    * using bitwise comparison.
    *
    * @param c The code point to search for.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
   inline int32_t indexOf(UChar32 c) const;
 
   /**
    * @stable ICU 2.0
    */
   inline int32_t indexOf(UChar32 c) const;
 
   /**

-   * Locate in this the first occurrence of the BMP code point <code>c</code>,
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the first occurrence of the BMP code point `c`,
+   * starting at offset `start`, using bitwise comparison.

    * @param c The code unit to search for.
    * @param start The offset at which searching will start.
    * @param c The code unit to search for.
    * @param start The offset at which searching will start.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int32_t indexOf(UChar c,
+  inline int32_t indexOf(char16_t c,

               int32_t start) const;
 
   /**
               int32_t start) const;
 
   /**

-   * Locate in this the first occurrence of the code point <TT>c</TT>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the first occurrence of the code point `c`
+   * starting at offset `start`, using bitwise comparison.

    *
    * @param c The code point to search for.
    * @param start The offset at which searching will start.
    *
    * @param c The code point to search for.
    * @param start The offset at which searching will start.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
   inline int32_t indexOf(UChar32 c,
               int32_t start) const;
 
   /**
    * @stable ICU 2.0
    */
   inline int32_t indexOf(UChar32 c,
               int32_t start) const;
 
   /**

-   * Locate in this the first occurrence of the BMP code point <code>c</code>
-   * in the range [<TT>start</TT>, <TT>start + length</TT>),
+   * Locate in this the first occurrence of the BMP code point `c`
+   * in the range [`start`, `start + length`),

    * using bitwise comparison.
    * @param c The code unit to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * using bitwise comparison.
    * @param c The code unit to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int32_t indexOf(UChar c,
+  inline int32_t indexOf(char16_t c,

               int32_t start,
               int32_t length) const;
 
   /**
               int32_t start,
               int32_t length) const;
 
   /**

-   * Locate in this the first occurrence of the code point <TT>c</TT>
-   * in the range [<TT>start</TT>, <TT>start + length</TT>),
+   * Locate in this the first occurrence of the code point `c`
+   * in the range [`start`, `start + length`),

    * using bitwise comparison.
    *
    * @param c The code point to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * using bitwise comparison.
    *
    * @param c The code point to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
   inline int32_t indexOf(UChar32 c,
    * @stable ICU 2.0
    */
   inline int32_t indexOf(UChar32 c,


@@ -1021,21 +1135,21 @@ public:
               int32_t length) const;
 
   /**
               int32_t length) const;
 
   /**

-   * Locate in this the last occurrence of the characters in <TT>text</TT>,
+   * Locate in this the last occurrence of the characters in `text`,

    * using bitwise comparison.
    * @param text The text to search for.
    * using bitwise comparison.
    * @param text The text to search for.

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(const UnicodeString& text) const;
 
   /**
    * or -1 if not found.
    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(const UnicodeString& text) const;
 
   /**

-   * Locate in this the last occurrence of the characters in <TT>text</TT>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the last occurrence of the characters in `text`
+   * starting at offset `start`, using bitwise comparison.

    * @param text The text to search for.
    * @param start The offset at which searching will start.
    * @param text The text to search for.
    * @param start The offset at which searching will start.

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */


@@ -1044,12 +1158,12 @@ public:
 
   /**
    * Locate in this the last occurrence in the range
 
   /**
    * Locate in this the last occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>text</TT>, using bitwise comparison.
+   * [`start`, `start + length`) of the characters
+   * in `text`, using bitwise comparison.

    * @param text The text to search for.
    * @param start The offset at which searching will start.
    * @param length The number of characters to search
    * @param text The text to search for.
    * @param start The offset at which searching will start.
    * @param length The number of characters to search

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */


@@ -1059,17 +1173,17 @@ public:
 
   /**
    * Locate in this the last occurrence in the range
 
   /**
    * Locate in this the last occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>),
+   * [`start`, `start + length`) of the characters
+   * in `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`),

    * using bitwise comparison.
    * @param srcText The text to search for.
    * using bitwise comparison.
    * @param srcText The text to search for.

-   * @param srcStart the offset into <TT>srcText</TT> at which
+   * @param srcStart the offset into `srcText` at which

    * to start matching
    * to start matching

-   * @param srcLength the number of characters in <TT>srcText</TT> to match
+   * @param srcLength the number of characters in `srcText` to match

    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */


@@ -1080,123 +1194,123 @@ public:
               int32_t length) const;
 
   /**
               int32_t length) const;
 
   /**

-   * Locate in this the last occurrence of the characters in <TT>srcChars</TT>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the last occurrence of the characters in `srcChars`
+   * starting at offset `start`, using bitwise comparison.

    * @param srcChars The text to search for.
    * @param srcChars The text to search for.

-   * @param srcLength the number of characters in <TT>srcChars</TT> to match
+   * @param srcLength the number of characters in `srcChars` to match

    * @param start the offset into this at which to start matching
    * @param start the offset into this at which to start matching

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */

-  inline int32_t lastIndexOf(const UChar *srcChars,
+  inline int32_t lastIndexOf(const char16_t *srcChars,

               int32_t srcLength,
               int32_t start) const;
 
   /**
    * Locate in this the last occurrence in the range
               int32_t srcLength,
               int32_t start) const;
 
   /**
    * Locate in this the last occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>srcChars</TT>, using bitwise comparison.
+   * [`start`, `start + length`) of the characters
+   * in `srcChars`, using bitwise comparison.

    * @param srcChars The text to search for.
    * @param srcChars The text to search for.

-   * @param srcLength the number of characters in <TT>srcChars</TT>
+   * @param srcLength the number of characters in `srcChars`

    * @param start The offset at which searching will start.
    * @param length The number of characters to search
    * @param start The offset at which searching will start.
    * @param length The number of characters to search

-   * @return The offset into this of the start of <TT>srcChars</TT>,
+   * @return The offset into this of the start of `srcChars`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */

-  inline int32_t lastIndexOf(const UChar *srcChars,
+  inline int32_t lastIndexOf(ConstChar16Ptr srcChars,

               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**
    * Locate in this the last occurrence in the range
               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**
    * Locate in this the last occurrence in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) of the characters
-   * in <TT>srcChars</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>),
+   * [`start`, `start + length`) of the characters
+   * in `srcChars` in the range
+   * [`srcStart`, `srcStart + srcLength`),

    * using bitwise comparison.
    * @param srcChars The text to search for.
    * using bitwise comparison.
    * @param srcChars The text to search for.

-   * @param srcStart the offset into <TT>srcChars</TT> at which
+   * @param srcStart the offset into `srcChars` at which

    * to start matching
    * to start matching

-   * @param srcLength the number of characters in <TT>srcChars</TT> to match
+   * @param srcLength the number of characters in `srcChars` to match

    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of the start of <TT>text</TT>,
+   * @return The offset into this of the start of `text`,

    * or -1 if not found.
    * @stable ICU 2.0
    */
    * or -1 if not found.
    * @stable ICU 2.0
    */

-  int32_t lastIndexOf(const UChar *srcChars,
+  int32_t lastIndexOf(const char16_t *srcChars,

               int32_t srcStart,
               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**
               int32_t srcStart,
               int32_t srcLength,
               int32_t start,
               int32_t length) const;
 
   /**

-   * Locate in this the last occurrence of the BMP code point <code>c</code>,
+   * Locate in this the last occurrence of the BMP code point `c`,

    * using bitwise comparison.
    * @param c The code unit to search for.
    * using bitwise comparison.
    * @param c The code unit to search for.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int32_t lastIndexOf(UChar c) const;
+  inline int32_t lastIndexOf(char16_t c) const;

 
   /**
 
   /**

-   * Locate in this the last occurrence of the code point <TT>c</TT>,
+   * Locate in this the last occurrence of the code point `c`,

    * using bitwise comparison.
    *
    * @param c The code point to search for.
    * using bitwise comparison.
    *
    * @param c The code point to search for.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(UChar32 c) const;
 
   /**
    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(UChar32 c) const;
 
   /**

-   * Locate in this the last occurrence of the BMP code point <code>c</code>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the last occurrence of the BMP code point `c`
+   * starting at offset `start`, using bitwise comparison.

    * @param c The code unit to search for.
    * @param start The offset at which searching will start.
    * @param c The code unit to search for.
    * @param start The offset at which searching will start.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int32_t lastIndexOf(UChar c,
+  inline int32_t lastIndexOf(char16_t c,

               int32_t start) const;
 
   /**
               int32_t start) const;
 
   /**

-   * Locate in this the last occurrence of the code point <TT>c</TT>
-   * starting at offset <TT>start</TT>, using bitwise comparison.
+   * Locate in this the last occurrence of the code point `c`
+   * starting at offset `start`, using bitwise comparison.

    *
    * @param c The code point to search for.
    * @param start The offset at which searching will start.
    *
    * @param c The code point to search for.
    * @param start The offset at which searching will start.

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(UChar32 c,
               int32_t start) const;
 
   /**
    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(UChar32 c,
               int32_t start) const;
 
   /**

-   * Locate in this the last occurrence of the BMP code point <code>c</code>
-   * in the range [<TT>start</TT>, <TT>start + length</TT>),
+   * Locate in this the last occurrence of the BMP code point `c`
+   * in the range [`start`, `start + length`),

    * using bitwise comparison.
    * @param c The code unit to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * using bitwise comparison.
    * @param c The code unit to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline int32_t lastIndexOf(UChar c,
+  inline int32_t lastIndexOf(char16_t c,

               int32_t start,
               int32_t length) const;
 
   /**
               int32_t start,
               int32_t length) const;
 
   /**

-   * Locate in this the last occurrence of the code point <TT>c</TT>
-   * in the range [<TT>start</TT>, <TT>start + length</TT>),
+   * Locate in this the last occurrence of the code point `c`
+   * in the range [`start`, `start + length`),

    * using bitwise comparison.
    *
    * @param c The code point to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search
    * using bitwise comparison.
    *
    * @param c The code point to search for.
    * @param start the offset into this at which to start matching
    * @param length the number of characters in this to search

-   * @return The offset into this of <TT>c</TT>, or -1 if not found.
+   * @return The offset into this of `c`, or -1 if not found.

    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(UChar32 c,
    * @stable ICU 2.0
    */
   inline int32_t lastIndexOf(UChar32 c,


@@ -1207,36 +1321,36 @@ public:
   /* Character access */
 
   /**
   /* Character access */
 
   /**

-   * Return the code unit at offset <tt>offset</tt>.
+   * Return the code unit at offset `offset`.

    * If the offset is not valid (0..length()-1) then U+ffff is returned.
    * @param offset a valid offset into the text
    * If the offset is not valid (0..length()-1) then U+ffff is returned.
    * @param offset a valid offset into the text

-   * @return the code unit at offset <tt>offset</tt>
+   * @return the code unit at offset `offset`

    *         or 0xffff if the offset is not valid for this string
    * @stable ICU 2.0
    */
    *         or 0xffff if the offset is not valid for this string
    * @stable ICU 2.0
    */

-  inline UChar charAt(int32_t offset) const;
+  inline char16_t charAt(int32_t offset) const;

 
   /**
 
   /**

-   * Return the code unit at offset <tt>offset</tt>.
+   * Return the code unit at offset `offset`.

    * If the offset is not valid (0..length()-1) then U+ffff is returned.
    * @param offset a valid offset into the text
    * If the offset is not valid (0..length()-1) then U+ffff is returned.
    * @param offset a valid offset into the text

-   * @return the code unit at offset <tt>offset</tt>
+   * @return the code unit at offset `offset`

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  inline UChar operator[] (int32_t offset) const;
+  inline char16_t operator[] (int32_t offset) const;

 
   /**
    * Return the code point that contains the code unit
 
   /**
    * Return the code point that contains the code unit

-   * at offset <tt>offset</tt>.
+   * at offset `offset`.

    * If the offset is not valid (0..length()-1) then U+ffff is returned.
    * @param offset a valid offset into the text
    * that indicates the text offset of any of the code units
    * that will be assembled into a code point (21-bit value) and returned
    * If the offset is not valid (0..length()-1) then U+ffff is returned.
    * @param offset a valid offset into the text
    * that indicates the text offset of any of the code units
    * that will be assembled into a code point (21-bit value) and returned

-   * @return the code point of text at <tt>offset</tt>
+   * @return the code point of text at `offset`

    *         or 0xffff if the offset is not valid for this string
    * @stable ICU 2.0
    */
    *         or 0xffff if the offset is not valid for this string
    * @stable ICU 2.0
    */

-  inline UChar32 char32At(int32_t offset) const;
+  UChar32 char32At(int32_t offset) const;

 
   /**
    * Adjust a random-access offset so that
 
   /**
    * Adjust a random-access offset so that


@@ -1253,7 +1367,7 @@ public:
    * @see U16_SET_CP_START
    * @stable ICU 2.0
    */
    * @see U16_SET_CP_START
    * @stable ICU 2.0
    */

-  inline int32_t getChar32Start(int32_t offset) const;
+  int32_t getChar32Start(int32_t offset) const;

 
   /**
    * Adjust a random-access offset so that
 
   /**
    * Adjust a random-access offset so that


@@ -1271,7 +1385,7 @@ public:
    * @see U16_SET_CP_LIMIT
    * @stable ICU 2.0
    */
    * @see U16_SET_CP_LIMIT
    * @stable ICU 2.0
    */

-  inline int32_t getChar32Limit(int32_t offset) const;
+  int32_t getChar32Limit(int32_t offset) const;

 
   /**
    * Move the code unit index along the string by delta code points.
 
   /**
    * Move the code unit index along the string by delta code points.


@@ -1289,33 +1403,33 @@ public:
    * This behaves like CharacterIterator::move32(delta, kCurrent).
    *
    * Behavior for out-of-bounds indexes:
    * This behaves like CharacterIterator::move32(delta, kCurrent).
    *
    * Behavior for out-of-bounds indexes:

-   * <code>moveIndex32</code> pins the input index to 0..length(), i.e.,
+   * `moveIndex32` pins the input index to 0..length(), i.e.,

    * if the input index<0 then it is pinned to 0;
    * if it is index>length() then it is pinned to length().
    * if the input index<0 then it is pinned to 0;
    * if it is index>length() then it is pinned to length().

-   * Afterwards, the index is moved by <code>delta</code> code points
+   * Afterwards, the index is moved by `delta` code points

    * forward or backward,
    * but no further backward than to 0 and no further forward than to length().
    * The resulting index return value will be in between 0 and length(), inclusively.
    *
    * Examples:
    * forward or backward,
    * but no further backward than to 0 and no further forward than to length().
    * The resulting index return value will be in between 0 and length(), inclusively.
    *
    * Examples:

-   * <pre>
-   * // s has code points 'a' U+10000 'b' U+10ffff U+2029
-   * UnicodeString s=UNICODE_STRING("a\\U00010000b\\U0010ffff\\u2029", 31).unescape();
+   * \code
+   *     // s has code points 'a' U+10000 'b' U+10ffff U+2029
+   *     UnicodeString s(u"a\U00010000b\U0010ffff\u2029");

    *
    *

-   * // initial index: position of U+10000
-   * int32_t index=1;
+   *     // initial index: position of U+10000
+   *     int32_t index=1;

    *
    *

-   * // the following examples will all result in index==4, position of U+10ffff
+   *     // the following examples will all result in index==4, position of U+10ffff

    *
    *

-   * // skip 2 code points from some position in the string
-   * index=s.moveIndex32(index, 2); // skips U+10000 and 'b'
+   *     // skip 2 code points from some position in the string
+   *     index=s.moveIndex32(index, 2); // skips U+10000 and 'b'

    *
    *

-   * // go to the 3rd code point from the start of s (0-based)
-   * index=s.moveIndex32(0, 3); // skips 'a', U+10000, and 'b'
+   *     // go to the 3rd code point from the start of s (0-based)
+   *     index=s.moveIndex32(0, 3); // skips 'a', U+10000, and 'b'

    *
    *

-   * // go to the next-to-last code point of s
-   * index=s.moveIndex32(s.length(), -2); // backward-skips U+2029 and U+10ffff
-   * </pre>
+   *     // go to the next-to-last code point of s
+   *     index=s.moveIndex32(s.length(), -2); // backward-skips U+2029 and U+10ffff
+   * \endcode

    *
    * @param index input code unit index
    * @param delta (signed) code point count to move the index forward or backward
    *
    * @param index input code unit index
    * @param delta (signed) code point count to move the index forward or backward


@@ -1329,22 +1443,22 @@ public:
 
   /**
    * Copy the characters in the range
 
   /**
    * Copy the characters in the range

-   * [<tt>start</tt>, <tt>start + length</tt>) into the array <tt>dst</tt>,
-   * beginning at <tt>dstStart</tt>.
-   * If the string aliases to <code>dst</code> itself as an external buffer,
+   * [`start`, `start + length`) into the array `dst`,
+   * beginning at `dstStart`.
+   * If the string aliases to `dst` itself as an external buffer,

    * then extract() will not copy the contents.
    *
    * @param start offset of first character which will be copied into the array
    * @param length the number of characters to extract
    * then extract() will not copy the contents.
    *
    * @param start offset of first character which will be copied into the array
    * @param length the number of characters to extract

-   * @param dst array in which to copy characters.  The length of <tt>dst</tt>
-   * must be at least (<tt>dstStart + length</tt>).
-   * @param dstStart the offset in <TT>dst</TT> where the first character
+   * @param dst array in which to copy characters.  The length of `dst`
+   * must be at least (`dstStart + length`).
+   * @param dstStart the offset in `dst` where the first character

    * will be extracted
    * @stable ICU 2.0
    */
   inline void extract(int32_t start,
            int32_t length,
    * will be extracted
    * @stable ICU 2.0
    */
   inline void extract(int32_t start,
            int32_t length,

-           UChar *dst,
+           Char16Ptr dst,

            int32_t dstStart = 0) const;
 
   /**
            int32_t dstStart = 0) const;
 
   /**


@@ -1359,27 +1473,26 @@ public:
    * If the string itself does not fit into dest
    * (length()>destCapacity) then the error code is set to U_BUFFER_OVERFLOW_ERROR.
    *
    * If the string itself does not fit into dest
    * (length()>destCapacity) then the error code is set to U_BUFFER_OVERFLOW_ERROR.
    *

-   * If the string aliases to <code>dest</code> itself as an external buffer,
+   * If the string aliases to `dest` itself as an external buffer,

    * then extract() will not copy the contents.
    *
    * @param dest Destination string buffer.
    * then extract() will not copy the contents.
    *
    * @param dest Destination string buffer.

-   * @param destCapacity Number of UChars available at dest.
+   * @param destCapacity Number of char16_ts available at dest.

    * @param errorCode ICU error code.
    * @return length()
    * @stable ICU 2.0
    */
   int32_t
    * @param errorCode ICU error code.
    * @return length()
    * @stable ICU 2.0
    */
   int32_t

-  extract(UChar *dest, int32_t destCapacity,
+  extract(Char16Ptr dest, int32_t destCapacity,

           UErrorCode &errorCode) const;
 
   /**
    * Copy the characters in the range
           UErrorCode &errorCode) const;
 
   /**
    * Copy the characters in the range

-   * [<tt>start</tt>, <tt>start + length</tt>) into the  UnicodeString
-   * <tt>target</tt>.
+   * [`start`, `start + length`) into the  UnicodeString
+   * `target`.

    * @param start offset of first character which will be copied
    * @param length the number of characters to extract
    * @param target UnicodeString into which to copy characters.
    * @param start offset of first character which will be copied
    * @param length the number of characters to extract
    * @param target UnicodeString into which to copy characters.

-   * @return A reference to <TT>target</TT>

    * @stable ICU 2.0
    */
   inline void extract(int32_t start,
    * @stable ICU 2.0
    */
   inline void extract(int32_t start,


@@ -1387,28 +1500,27 @@ public:
            UnicodeString& target) const;
 
   /**
            UnicodeString& target) const;
 
   /**

-   * Copy the characters in the range [<tt>start</tt>, <tt>limit</tt>)
-   * into the array <tt>dst</tt>, beginning at <tt>dstStart</tt>.
+   * Copy the characters in the range [`start`, `limit`)
+   * into the array `dst`, beginning at `dstStart`.

    * @param start offset of first character which will be copied into the array
    * @param limit offset immediately following the last character to be copied
    * @param start offset of first character which will be copied into the array
    * @param limit offset immediately following the last character to be copied

-   * @param dst array in which to copy characters.  The length of <tt>dst</tt>
-   * must be at least (<tt>dstStart + (limit - start)</tt>).
-   * @param dstStart the offset in <TT>dst</TT> where the first character
+   * @param dst array in which to copy characters.  The length of `dst`
+   * must be at least (`dstStart + (limit - start)`).
+   * @param dstStart the offset in `dst` where the first character

    * will be extracted
    * @stable ICU 2.0
    */
   inline void extractBetween(int32_t start,
               int32_t limit,
    * will be extracted
    * @stable ICU 2.0
    */
   inline void extractBetween(int32_t start,
               int32_t limit,

-              UChar *dst,
+              char16_t *dst,

               int32_t dstStart = 0) const;
 
   /**
               int32_t dstStart = 0) const;
 
   /**

-   * Copy the characters in the range [<tt>start</tt>, <tt>limit</tt>)
-   * into the UnicodeString <tt>target</tt>.  Replaceable API.
+   * Copy the characters in the range [`start`, `limit`)
+   * into the UnicodeString `target`.  Replaceable API.

    * @param start offset of first character which will be copied
    * @param limit offset immediately following the last character to be copied
    * @param target UnicodeString into which to copy characters.
    * @param start offset of first character which will be copied
    * @param limit offset immediately following the last character to be copied
    * @param target UnicodeString into which to copy characters.

-   * @return A reference to <TT>target</TT>

    * @stable ICU 2.0
    */
   virtual void extractBetween(int32_t start,
    * @stable ICU 2.0
    */
   virtual void extractBetween(int32_t start,


@@ -1416,12 +1528,12 @@ public:
               UnicodeString& target) const;
 
   /**
               UnicodeString& target) const;
 
   /**

-   * Copy the characters in the range 
-   * [<tt>start</TT>, <tt>start + length</TT>) into an array of characters.
+   * Copy the characters in the range
+   * [`start`, `start + startLength`) into an array of characters.

    * All characters must be invariant (see utypes.h).
    * Use US_INV as the last, signature-distinguishing parameter.
    *
    * All characters must be invariant (see utypes.h).
    * Use US_INV as the last, signature-distinguishing parameter.
    *

-   * This function does not write any more than <code>targetLength</code>
+   * This function does not write any more than `targetCapacity`

    * characters but returns the length of the entire output string
    * so that one can allocate a larger buffer and call the function again
    * if necessary.
    * characters but returns the length of the entire output string
    * so that one can allocate a larger buffer and call the function again
    * if necessary.


@@ -1434,7 +1546,7 @@ public:
    * @param targetCapacity the length of the target buffer
    * @param inv Signature-distinguishing paramater, use US_INV.
    * @return the output string length, not including the terminating NUL
    * @param targetCapacity the length of the target buffer
    * @param inv Signature-distinguishing paramater, use US_INV.
    * @return the output string length, not including the terminating NUL

-   * @draft ICU 3.2
+   * @stable ICU 3.2

    */
   int32_t extract(int32_t start,
            int32_t startLength,
    */
   int32_t extract(int32_t start,
            int32_t startLength,


@@ -1442,11 +1554,39 @@ public:
            int32_t targetCapacity,
            enum EInvariant inv) const;
 
            int32_t targetCapacity,
            enum EInvariant inv) const;
 

+#if U_CHARSET_IS_UTF8 || !UCONFIG_NO_CONVERSION
+
+  /**
+   * Copy the characters in the range
+   * [`start`, `start + length`) into an array of characters
+   * in the platform's default codepage.
+   * This function does not write any more than `targetLength`
+   * characters but returns the length of the entire output string
+   * so that one can allocate a larger buffer and call the function again
+   * if necessary.
+   * The output string is NUL-terminated if possible.
+   *
+   * @param start offset of first character which will be copied
+   * @param startLength the number of characters to extract
+   * @param target the target buffer for extraction
+   * @param targetLength the length of the target buffer
+   * If `target` is NULL, then the number of bytes required for
+   * `target` is returned.
+   * @return the output string length, not including the terminating NUL
+   * @stable ICU 2.0
+   */
+  int32_t extract(int32_t start,
+           int32_t startLength,
+           char *target,
+           uint32_t targetLength) const;
+
+#endif
+

 #if !UCONFIG_NO_CONVERSION
 
   /**
    * Copy the characters in the range
 #if !UCONFIG_NO_CONVERSION
 
   /**
    * Copy the characters in the range

-   * [<tt>start</TT>, <tt>start + length</TT>) into an array of characters
+   * [`start`, `start + length`) into an array of characters

    * in a specified codepage.
    * The output string is NUL-terminated.
    *
    * in a specified codepage.
    * The output string is NUL-terminated.
    *


@@ -1460,11 +1600,11 @@ public:
    * @param target the target buffer for extraction
    * @param codepage the desired codepage for the characters.  0 has
    * the special meaning of the default codepage
    * @param target the target buffer for extraction
    * @param codepage the desired codepage for the characters.  0 has
    * the special meaning of the default codepage

-   * If <code>codepage</code> is an empty string (<code>""</code>),
+   * If `codepage` is an empty string (`""`),

    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.

-   * If <TT>target</TT> is NULL, then the number of bytes required for
-   * <TT>target</TT> is returned. It is assumed that the target is big enough
+   * If `target` is NULL, then the number of bytes required for
+   * `target` is returned. It is assumed that the target is big enough

    * to fit all of the characters.
    * @return the output string length, not including the terminating NUL
    * @stable ICU 2.0
    * to fit all of the characters.
    * @return the output string length, not including the terminating NUL
    * @stable ICU 2.0


@@ -1476,9 +1616,9 @@ public:
 
   /**
    * Copy the characters in the range
 
   /**
    * Copy the characters in the range

-   * [<tt>start</TT>, <tt>start + length</TT>) into an array of characters
+   * [`start`, `start + length`) into an array of characters

    * in a specified codepage.
    * in a specified codepage.

-   * This function does not write any more than <code>targetLength</code>
+   * This function does not write any more than `targetLength`

    * characters but returns the length of the entire output string
    * so that one can allocate a larger buffer and call the function again
    * if necessary.
    * characters but returns the length of the entire output string
    * so that one can allocate a larger buffer and call the function again
    * if necessary.


@@ -1495,11 +1635,11 @@ public:
    * @param targetLength the length of the target buffer
    * @param codepage the desired codepage for the characters.  0 has
    * the special meaning of the default codepage
    * @param targetLength the length of the target buffer
    * @param codepage the desired codepage for the characters.  0 has
    * the special meaning of the default codepage

-   * If <code>codepage</code> is an empty string (<code>""</code>),
+   * If `codepage` is an empty string (`""`),

    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.

-   * If <TT>target</TT> is NULL, then the number of bytes required for
-   * <TT>target</TT> is returned.
+   * If `target` is NULL, then the number of bytes required for
+   * `target` is returned.

    * @return the output string length, not including the terminating NUL
    * @stable ICU 2.0
    */
    * @return the output string length, not including the terminating NUL
    * @stable ICU 2.0
    */


@@ -1507,7 +1647,7 @@ public:
            int32_t startLength,
            char *target,
            uint32_t targetLength,
            int32_t startLength,
            char *target,
            uint32_t targetLength,

-           const char *codepage = 0) const;
+           const char *codepage) const;

 
   /**
    * Convert the UnicodeString into a codepage string using an existing UConverter.
 
   /**
    * Convert the UnicodeString into a codepage string using an existing UConverter.


@@ -1532,11 +1672,87 @@ public:
 
 #endif
 
 
 #endif
 

+  /**
+   * Create a temporary substring for the specified range.
+   * Unlike the substring constructor and setTo() functions,
+   * the object returned here will be a read-only alias (using getBuffer())
+   * rather than copying the text.
+   * As a result, this substring operation is much faster but requires
+   * that the original string not be modified or deleted during the lifetime
+   * of the returned substring object.
+   * @param start offset of the first character visible in the substring
+   * @param length length of the substring
+   * @return a read-only alias UnicodeString object for the substring
+   * @stable ICU 4.4
+   */
+  UnicodeString tempSubString(int32_t start=0, int32_t length=INT32_MAX) const;
+
+  /**
+   * Create a temporary substring for the specified range.
+   * Same as tempSubString(start, length) except that the substring range
+   * is specified as a (start, limit) pair (with an exclusive limit index)
+   * rather than a (start, length) pair.
+   * @param start offset of the first character visible in the substring
+   * @param limit offset immediately following the last character visible in the substring
+   * @return a read-only alias UnicodeString object for the substring
+   * @stable ICU 4.4
+   */
+  inline UnicodeString tempSubStringBetween(int32_t start, int32_t limit=INT32_MAX) const;
+
+  /**
+   * Convert the UnicodeString to UTF-8 and write the result
+   * to a ByteSink. This is called by toUTF8String().
+   * Unpaired surrogates are replaced with U+FFFD.
+   * Calls u_strToUTF8WithSub().
+   *
+   * @param sink A ByteSink to which the UTF-8 version of the string is written.
+   *             sink.Flush() is called at the end.
+   * @stable ICU 4.2
+   * @see toUTF8String
+   */
+  void toUTF8(ByteSink &sink) const;
+
+  /**
+   * Convert the UnicodeString to UTF-8 and append the result
+   * to a standard string.
+   * Unpaired surrogates are replaced with U+FFFD.
+   * Calls toUTF8().
+   *
+   * @param result A standard string (or a compatible object)
+   *        to which the UTF-8 version of the string is appended.
+   * @return The string object.
+   * @stable ICU 4.2
+   * @see toUTF8
+   */
+  template<typename StringClass>
+  StringClass &toUTF8String(StringClass &result) const {
+    StringByteSink<StringClass> sbs(&result, length());
+    toUTF8(sbs);
+    return result;
+  }
+
+  /**
+   * Convert the UnicodeString to UTF-32.
+   * Unpaired surrogates are replaced with U+FFFD.
+   * Calls u_strToUTF32WithSub().
+   *
+   * @param utf32 destination string buffer, can be NULL if capacity==0
+   * @param capacity the number of UChar32s available at utf32
+   * @param errorCode Standard ICU error code. Its input value must
+   *                  pass the U_SUCCESS() test, or else the function returns
+   *                  immediately. Check for U_FAILURE() on output or use with
+   *                  function chaining. (See User Guide for details.)
+   * @return The length of the UTF-32 string.
+   * @see fromUTF32
+   * @stable ICU 4.2
+   */
+  int32_t toUTF32(UChar32 *utf32, int32_t capacity, UErrorCode &errorCode) const;
+

   /* Length operations */
 
   /**
    * Return the length of the UnicodeString object.
   /* Length operations */
 
   /**
    * Return the length of the UnicodeString object.

-   * The length is the number of UChar code units are in the UnicodeString.
+   * The length is the number of char16_t code units are in the UnicodeString.

    * If you want the number of code points, please use countChar32().
    * @return the length of the UnicodeString object
    * @see countChar32
    * If you want the number of code points, please use countChar32().
    * @return the length of the UnicodeString object
    * @see countChar32


@@ -1545,14 +1761,14 @@ public:
   inline int32_t length(void) const;
 
   /**
   inline int32_t length(void) const;
 
   /**

-   * Count Unicode code points in the length UChar code units of the string.
-   * A code point may occupy either one or two UChar code units.
+   * Count Unicode code points in the length char16_t code units of the string.
+   * A code point may occupy either one or two char16_t code units.

    * Counting code points involves reading all code units.
    *
    * This functions is basically the inverse of moveIndex32().
    *
    * @param start the index of the first code unit to check
    * Counting code points involves reading all code units.
    *
    * This functions is basically the inverse of moveIndex32().
    *
    * @param start the index of the first code unit to check

-   * @param length the number of UChar code units to check
+   * @param length the number of char16_t code units to check

    * @return the number of code points in the specified code units
    * @see length
    * @stable ICU 2.0
    * @return the number of code points in the specified code units
    * @see length
    * @stable ICU 2.0


@@ -1561,7 +1777,7 @@ public:
   countChar32(int32_t start=0, int32_t length=INT32_MAX) const;
 
   /**
   countChar32(int32_t start=0, int32_t length=INT32_MAX) const;
 
   /**

-   * Check if the length UChar code units of the string
+   * Check if the length char16_t code units of the string

    * contain more Unicode code points than a certain number.
    * This is more efficient than counting all code points in this part of the string
    * and comparing that number with a threshold.
    * contain more Unicode code points than a certain number.
    * This is more efficient than counting all code points in this part of the string
    * and comparing that number with a threshold.


@@ -1569,10 +1785,10 @@ public:
    * falls within a certain range, and
    * never needs to count more than 'number+1' code points.
    * Logically equivalent to (countChar32(start, length)>number).
    * falls within a certain range, and
    * never needs to count more than 'number+1' code points.
    * Logically equivalent to (countChar32(start, length)>number).

-   * A Unicode code point may occupy either one or two UChar code units.
+   * A Unicode code point may occupy either one or two char16_t code units.

    *
    * @param start the index of the first code unit to check (0 for the entire string)
    *
    * @param start the index of the first code unit to check (0 for the entire string)

-   * @param length the number of UChar code units to check
+   * @param length the number of char16_t code units to check

    *               (use INT32_MAX for the entire string; remember that start/length
    *                values are pinned)
    * @param number The number of code points in the (sub)string is compared against
    *               (use INT32_MAX for the entire string; remember that start/length
    *                values are pinned)
    * @param number The number of code points in the (sub)string is compared against


@@ -1598,7 +1814,7 @@ public:
    * This is useful together with the getBuffer functions.
    * See there for details.
    *
    * This is useful together with the getBuffer functions.
    * See there for details.
    *

-   * @return the number of UChars available in the internal buffer
+   * @return the number of char16_ts available in the internal buffer

    * @see getBuffer
    * @stable ICU 2.0
    */
    * @see getBuffer
    * @stable ICU 2.0
    */


@@ -1615,12 +1831,13 @@ public:
 
   /**
    * Determine if this object contains a valid string.
 
   /**
    * Determine if this object contains a valid string.

-   * A bogus string has no value. It is different from an empty string.
-   * It can be used to indicate that no string value is available.
-   * getBuffer() and getTerminatedBuffer() return NULL, and
+   * A bogus string has no value. It is different from an empty string,
+   * although in both cases isEmpty() returns TRUE and length() returns 0.
+   * setToBogus() and isBogus() can be used to indicate that no string value is available.
+   * For a bogus string, getBuffer() and getTerminatedBuffer() return NULL, and

    * length() returns 0.
    *
    * length() returns 0.
    *

-   * @return TRUE if the string is valid, FALSE otherwise
+   * @return TRUE if the string is bogus/invalid, FALSE otherwise

    * @see setToBogus()
    * @stable ICU 2.0
    */
    * @see setToBogus()
    * @stable ICU 2.0
    */


@@ -1635,28 +1852,44 @@ public:
 
   /**
    * Assignment operator.  Replace the characters in this UnicodeString
 
   /**
    * Assignment operator.  Replace the characters in this UnicodeString

-   * with the characters from <TT>srcText</TT>.
+   * with the characters from `srcText`.
+   *
+   * Starting with ICU 2.4, the assignment operator and the copy constructor
+   * allocate a new buffer and copy the buffer contents even for readonly aliases.
+   * By contrast, the fastCopyFrom() function implements the old,
+   * more efficient but less safe behavior
+   * of making this string also a readonly alias to the same buffer.
+   *
+   * If the source object has an "open" buffer from getBuffer(minCapacity),
+   * then the copy is an empty string.
+   *

    * @param srcText The text containing the characters to replace
    * @return a reference to this
    * @stable ICU 2.0
    * @param srcText The text containing the characters to replace
    * @return a reference to this
    * @stable ICU 2.0

+   * @see fastCopyFrom

    */
   UnicodeString &operator=(const UnicodeString &srcText);
 
   /**
    * Almost the same as the assignment operator.
    * Replace the characters in this UnicodeString
    */
   UnicodeString &operator=(const UnicodeString &srcText);
 
   /**
    * Almost the same as the assignment operator.
    * Replace the characters in this UnicodeString

-   * with the characters from <code>srcText</code>.
+   * with the characters from `srcText`.
+   *
+   * This function works the same as the assignment operator
+   * for all strings except for ones that are readonly aliases.

    *
    *

-   * This function works the same for all strings except for ones that
-   * are readonly aliases.

    * Starting with ICU 2.4, the assignment operator and the copy constructor
    * allocate a new buffer and copy the buffer contents even for readonly aliases.
    * This function implements the old, more efficient but less safe behavior
    * of making this string also a readonly alias to the same buffer.
    * Starting with ICU 2.4, the assignment operator and the copy constructor
    * allocate a new buffer and copy the buffer contents even for readonly aliases.
    * This function implements the old, more efficient but less safe behavior
    * of making this string also a readonly alias to the same buffer.

+   *

    * The fastCopyFrom function must be used only if it is known that the lifetime of
    * The fastCopyFrom function must be used only if it is known that the lifetime of

-   * this UnicodeString is at least as long as the lifetime of the aliased buffer
+   * this UnicodeString does not exceed the lifetime of the aliased buffer

    * including its contents, for example for strings from resource bundles
    * including its contents, for example for strings from resource bundles

-   * or aliases to string contents.
+   * or aliases to string constants.
+   *
+   * If the source object has an "open" buffer from getBuffer(minCapacity),
+   * then the copy is an empty string.

    *
    * @param src The text containing the characters to replace.
    * @return a reference to this
    *
    * @param src The text containing the characters to replace.
    * @return a reference to this


@@ -1664,18 +1897,46 @@ public:
    */
   UnicodeString &fastCopyFrom(const UnicodeString &src);
 
    */
   UnicodeString &fastCopyFrom(const UnicodeString &src);
 

+  /**
+   * Move assignment operator; might leave src in bogus state.
+   * This string will have the same contents and state that the source string had.
+   * The behavior is undefined if *this and src are the same object.
+   * @param src source string
+   * @return *this
+   * @stable ICU 56
+   */
+  UnicodeString &operator=(UnicodeString &&src) U_NOEXCEPT;
+
+  /**
+   * Swap strings.
+   * @param other other string
+   * @stable ICU 56
+   */
+  void swap(UnicodeString &other) U_NOEXCEPT;
+
+  /**
+   * Non-member UnicodeString swap function.
+   * @param s1 will get s2's contents and state
+   * @param s2 will get s1's contents and state
+   * @stable ICU 56
+   */
+  friend inline void U_EXPORT2
+  swap(UnicodeString &s1, UnicodeString &s2) U_NOEXCEPT {
+    s1.swap(s2);
+  }
+

   /**
    * Assignment operator.  Replace the characters in this UnicodeString
   /**
    * Assignment operator.  Replace the characters in this UnicodeString

-   * with the code unit <TT>ch</TT>.
+   * with the code unit `ch`.

    * @param ch the code unit to replace
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param ch the code unit to replace
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& operator= (UChar ch);
+  inline UnicodeString& operator= (char16_t ch);

 
   /**
    * Assignment operator.  Replace the characters in this UnicodeString
 
   /**
    * Assignment operator.  Replace the characters in this UnicodeString

-   * with the code point <TT>ch</TT>.
+   * with the code point `ch`.

    * @param ch the code point to replace
    * @return a reference to this
    * @stable ICU 2.0
    * @param ch the code point to replace
    * @return a reference to this
    * @stable ICU 2.0


@@ -1684,11 +1945,11 @@ public:
 
   /**
    * Set the text in the UnicodeString object to the characters
 
   /**
    * Set the text in the UnicodeString object to the characters

-   * in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcText.length()</TT>).
-   * <TT>srcText</TT> is not modified.
+   * in `srcText` in the range
+   * [`srcStart`, `srcText.length()`).
+   * `srcText` is not modified.

    * @param srcText the source for the new characters
    * @param srcText the source for the new characters

-   * @param srcStart the offset into <TT>srcText</TT> where new characters
+   * @param srcStart the offset into `srcText` where new characters

    * will be obtained
    * @return a reference to this
    * @stable ICU 2.2
    * will be obtained
    * @return a reference to this
    * @stable ICU 2.2


@@ -1698,13 +1959,13 @@ public:
 
   /**
    * Set the text in the UnicodeString object to the characters
 
   /**
    * Set the text in the UnicodeString object to the characters

-   * in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
-   * <TT>srcText</TT> is not modified.
+   * in `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`).
+   * `srcText` is not modified.

    * @param srcText the source for the new characters
    * @param srcText the source for the new characters

-   * @param srcStart the offset into <TT>srcText</TT> where new characters
+   * @param srcStart the offset into `srcText` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcText</TT> in the
+   * @param srcLength the number of characters in `srcText` in the

    * replace string.
    * @return a reference to this
    * @stable ICU 2.0
    * replace string.
    * @return a reference to this
    * @stable ICU 2.0


@@ -1715,8 +1976,8 @@ public:
 
   /**
    * Set the text in the UnicodeString object to the characters in
 
   /**
    * Set the text in the UnicodeString object to the characters in

-   * <TT>srcText</TT>.
-   * <TT>srcText</TT> is not modified.
+   * `srcText`.
+   * `srcText` is not modified.

    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0
    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0


@@ -1725,61 +1986,64 @@ public:
 
   /**
    * Set the characters in the UnicodeString object to the characters
 
   /**
    * Set the characters in the UnicodeString object to the characters

-   * in <TT>srcChars</TT>. <TT>srcChars</TT> is not modified.
+   * in `srcChars`. `srcChars` is not modified.

    * @param srcChars the source for the new characters
    * @param srcLength the number of Unicode characters in srcChars.
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcChars the source for the new characters
    * @param srcLength the number of Unicode characters in srcChars.
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& setTo(const UChar *srcChars,
+  inline UnicodeString& setTo(const char16_t *srcChars,

                int32_t srcLength);
 
   /**
    * Set the characters in the UnicodeString object to the code unit
                int32_t srcLength);
 
   /**
    * Set the characters in the UnicodeString object to the code unit

-   * <TT>srcChar</TT>.
+   * `srcChar`.

    * @param srcChar the code unit which becomes the UnicodeString's character
    * content
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcChar the code unit which becomes the UnicodeString's character
    * content
    * @return a reference to this
    * @stable ICU 2.0
    */

-  UnicodeString& setTo(UChar srcChar);
+  inline UnicodeString& setTo(char16_t srcChar);

 
   /**
    * Set the characters in the UnicodeString object to the code point
 
   /**
    * Set the characters in the UnicodeString object to the code point

-   * <TT>srcChar</TT>.
+   * `srcChar`.

    * @param srcChar the code point which becomes the UnicodeString's character
    * content
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcChar the code point which becomes the UnicodeString's character
    * content
    * @return a reference to this
    * @stable ICU 2.0
    */

-  UnicodeString& setTo(UChar32 srcChar);
+  inline UnicodeString& setTo(UChar32 srcChar);

 
   /**
 
   /**

-   * Aliasing setTo() function, analogous to the readonly-aliasing UChar* constructor.
+   * Aliasing setTo() function, analogous to the readonly-aliasing char16_t* constructor.

    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has copy-on-write semantics:
    * When the string is modified, then the buffer is first copied into
    * newly allocated memory.
    * The aliased buffer is never modified.
    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has copy-on-write semantics:
    * When the string is modified, then the buffer is first copied into
    * newly allocated memory.
    * The aliased buffer is never modified.

-   * In an assignment to another UnicodeString, the text will be aliased again,
+   *
+   * In an assignment to another UnicodeString, when using the copy constructor
+   * or the assignment operator, the text will be copied.
+   * When using fastCopyFrom(), the text will be aliased again,

    * so that both strings then alias the same readonly-text.
    *
    * so that both strings then alias the same readonly-text.
    *

-   * @param isTerminated specifies if <code>text</code> is <code>NUL</code>-terminated.
-   *                     This must be true if <code>textLength==-1</code>.
+   * @param isTerminated specifies if `text` is `NUL`-terminated.
+   *                     This must be true if `textLength==-1`.

    * @param text The characters to alias for the UnicodeString.
    * @param text The characters to alias for the UnicodeString.

-   * @param textLength The number of Unicode characters in <code>text</code> to alias.
+   * @param textLength The number of Unicode characters in `text` to alias.

    *                   If -1, then this constructor will determine the length
    *                   If -1, then this constructor will determine the length

-   *                   by calling <code>u_strlen()</code>.
+   *                   by calling `u_strlen()`.

    * @return a reference to this
    * @stable ICU 2.0
    */
   UnicodeString &setTo(UBool isTerminated,
    * @return a reference to this
    * @stable ICU 2.0
    */
   UnicodeString &setTo(UBool isTerminated,

-                       const UChar *text,
+                       ConstChar16Ptr text,

                        int32_t textLength);
 
   /**
                        int32_t textLength);
 
   /**

-   * Aliasing setTo() function, analogous to the writable-aliasing UChar* constructor.
+   * Aliasing setTo() function, analogous to the writable-aliasing char16_t* constructor.

    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has write-through semantics:
    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has write-through semantics:


@@ -1788,16 +2052,16 @@ public:
    * a new buffer will be allocated and the contents copied as with regularly
    * constructed strings.
    * In an assignment to another UnicodeString, the buffer will be copied.
    * a new buffer will be allocated and the contents copied as with regularly
    * constructed strings.
    * In an assignment to another UnicodeString, the buffer will be copied.

-   * The extract(UChar *dst) function detects whether the dst pointer is the same
+   * The extract(Char16Ptr dst) function detects whether the dst pointer is the same

    * as the string buffer itself and will in this case not copy the contents.
    *
    * @param buffer The characters to alias for the UnicodeString.
    * as the string buffer itself and will in this case not copy the contents.
    *
    * @param buffer The characters to alias for the UnicodeString.

-   * @param buffLength The number of Unicode characters in <code>buffer</code> to alias.
-   * @param buffCapacity The size of <code>buffer</code> in UChars.
+   * @param buffLength The number of Unicode characters in `buffer` to alias.
+   * @param buffCapacity The size of `buffer` in char16_ts.

    * @return a reference to this
    * @stable ICU 2.0
    */
    * @return a reference to this
    * @stable ICU 2.0
    */

-  UnicodeString &setTo(UChar *buffer,
+  UnicodeString &setTo(char16_t *buffer,

                        int32_t buffLength,
                        int32_t buffCapacity);
 
                        int32_t buffLength,
                        int32_t buffCapacity);
 


@@ -1833,7 +2097,7 @@ public:
    *   s.truncate(0);        // set to an empty string (complete truncation), or
    *   s=UnicodeString();    // assign an empty string, or
    *   s.setTo((UChar32)-1); // set to a pseudo code point that is out of range, or
    *   s.truncate(0);        // set to an empty string (complete truncation), or
    *   s=UnicodeString();    // assign an empty string, or
    *   s.setTo((UChar32)-1); // set to a pseudo code point that is out of range, or

-   *   static const UChar nul=0;
+   *   static const char16_t nul=0;

    *   s.setTo(&nul, 0);     // set to an empty C Unicode string
    * }
    * \endcode
    *   s.setTo(&nul, 0);     // set to an empty C Unicode string
    * }
    * \endcode


@@ -1851,22 +2115,22 @@ public:
    * @stable ICU 2.0
    */
   UnicodeString& setCharAt(int32_t offset,
    * @stable ICU 2.0
    */
   UnicodeString& setCharAt(int32_t offset,

-               UChar ch);
+               char16_t ch);

 
 
   /* Append operations */
 
   /**
 
 
   /* Append operations */
 
   /**

-   * Append operator. Append the code unit <TT>ch</TT> to the UnicodeString
+   * Append operator. Append the code unit `ch` to the UnicodeString

    * object.
    * @param ch the code unit to be appended
    * @return a reference to this
    * @stable ICU 2.0
    */
    * object.
    * @param ch the code unit to be appended
    * @return a reference to this
    * @stable ICU 2.0
    */

- inline  UnicodeString& operator+= (UChar ch);
+ inline  UnicodeString& operator+= (char16_t ch);

 
   /**
 
   /**

-   * Append operator. Append the code point <TT>ch</TT> to the UnicodeString
+   * Append operator. Append the code point `ch` to the UnicodeString

    * object.
    * @param ch the code point to be appended
    * @return a reference to this
    * object.
    * @param ch the code point to be appended
    * @return a reference to this


@@ -1875,9 +2139,8 @@ public:
  inline  UnicodeString& operator+= (UChar32 ch);
 
   /**
  inline  UnicodeString& operator+= (UChar32 ch);
 
   /**

-   * Append operator. Append the characters in <TT>srcText</TT> to the
-   * UnicodeString object at offset <TT>start</TT>. <TT>srcText</TT> is
-   * not modified.
+   * Append operator. Append the characters in `srcText` to the
+   * UnicodeString object. `srcText` is not modified.

    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0
    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0


@@ -1886,14 +2149,14 @@ public:
 
   /**
    * Append the characters
 
   /**
    * Append the characters

-   * in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>) to the
-   * UnicodeString object at offset <TT>start</TT>. <TT>srcText</TT>
+   * in `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`) to the
+   * UnicodeString object at offset `start`. `srcText`

    * is not modified.
    * @param srcText the source for the new characters
    * is not modified.
    * @param srcText the source for the new characters

-   * @param srcStart the offset into <TT>srcText</TT> where new characters
+   * @param srcStart the offset into `srcText` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcText</TT> in
+   * @param srcLength the number of characters in `srcText` in

    * the append string
    * @return a reference to this
    * @stable ICU 2.0
    * the append string
    * @return a reference to this
    * @stable ICU 2.0


@@ -1903,8 +2166,8 @@ public:
             int32_t srcLength);
 
   /**
             int32_t srcLength);
 
   /**

-   * Append the characters in <TT>srcText</TT> to the UnicodeString object at
-   * offset <TT>start</TT>. <TT>srcText</TT> is not modified.
+   * Append the characters in `srcText` to the UnicodeString object.
+   * `srcText` is not modified.

    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0
    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0


@@ -1912,61 +2175,62 @@ public:
   inline UnicodeString& append(const UnicodeString& srcText);
 
   /**
   inline UnicodeString& append(const UnicodeString& srcText);
 
   /**

-   * Append the characters in <TT>srcChars</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>) to the UnicodeString
+   * Append the characters in `srcChars` in the range
+   * [`srcStart`, `srcStart + srcLength`) to the UnicodeString

    * object at offset
    * object at offset

-   * <TT>start</TT>. <TT>srcChars</TT> is not modified.
+   * `start`. `srcChars` is not modified.

    * @param srcChars the source for the new characters
    * @param srcChars the source for the new characters

-   * @param srcStart the offset into <TT>srcChars</TT> where new characters
+   * @param srcStart the offset into `srcChars` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcChars</TT> in
-   * the append string
+   * @param srcLength the number of characters in `srcChars` in
+   *                  the append string; can be -1 if `srcChars` is NUL-terminated

    * @return a reference to this
    * @stable ICU 2.0
    */
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& append(const UChar *srcChars,
+  inline UnicodeString& append(const char16_t *srcChars,

             int32_t srcStart,
             int32_t srcLength);
 
   /**
             int32_t srcStart,
             int32_t srcLength);
 
   /**

-   * Append the characters in <TT>srcChars</TT> to the UnicodeString object
-   * at offset <TT>start</TT>. <TT>srcChars</TT> is not modified.
+   * Append the characters in `srcChars` to the UnicodeString object
+   * at offset `start`. `srcChars` is not modified.

    * @param srcChars the source for the new characters
    * @param srcChars the source for the new characters

-   * @param srcLength the number of Unicode characters in <TT>srcChars</TT>
+   * @param srcLength the number of Unicode characters in `srcChars`;
+   *                  can be -1 if `srcChars` is NUL-terminated

    * @return a reference to this
    * @stable ICU 2.0
    */
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& append(const UChar *srcChars,
+  inline UnicodeString& append(ConstChar16Ptr srcChars,

             int32_t srcLength);
 
   /**
             int32_t srcLength);
 
   /**

-   * Append the code unit <TT>srcChar</TT> to the UnicodeString object.
+   * Append the code unit `srcChar` to the UnicodeString object.

    * @param srcChar the code unit to append
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcChar the code unit to append
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& append(UChar srcChar);
+  inline UnicodeString& append(char16_t srcChar);

 
   /**
 
   /**

-   * Append the code point <TT>srcChar</TT> to the UnicodeString object.
+   * Append the code point `srcChar` to the UnicodeString object.

    * @param srcChar the code point to append
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcChar the code point to append
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& append(UChar32 srcChar);
+  UnicodeString& append(UChar32 srcChar);

 
 
   /* Insert operations */
 
   /**
 
 
   /* Insert operations */
 
   /**

-   * Insert the characters in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>) into the UnicodeString
-   * object at offset <TT>start</TT>. <TT>srcText</TT> is not modified.
+   * Insert the characters in `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`) into the UnicodeString
+   * object at offset `start`. `srcText` is not modified.

    * @param start the offset where the insertion begins
    * @param srcText the source for the new characters
    * @param start the offset where the insertion begins
    * @param srcText the source for the new characters

-   * @param srcStart the offset into <TT>srcText</TT> where new characters
+   * @param srcStart the offset into `srcText` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcText</TT> in
+   * @param srcLength the number of characters in `srcText` in

    * the insert string
    * @return a reference to this
    * @stable ICU 2.0
    * the insert string
    * @return a reference to this
    * @stable ICU 2.0


@@ -1977,8 +2241,8 @@ public:
             int32_t srcLength);
 
   /**
             int32_t srcLength);
 
   /**

-   * Insert the characters in <TT>srcText</TT> into the UnicodeString object
-   * at offset <TT>start</TT>. <TT>srcText</TT> is not modified.
+   * Insert the characters in `srcText` into the UnicodeString object
+   * at offset `start`. `srcText` is not modified.

    * @param start the offset where the insertion begins
    * @param srcText the source for the new characters
    * @return a reference to this
    * @param start the offset where the insertion begins
    * @param srcText the source for the new characters
    * @return a reference to this


@@ -1988,26 +2252,26 @@ public:
             const UnicodeString& srcText);
 
   /**
             const UnicodeString& srcText);
 
   /**

-   * Insert the characters in <TT>srcChars</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>) into the UnicodeString
-   *  object at offset <TT>start</TT>. <TT>srcChars</TT> is not modified.
+   * Insert the characters in `srcChars` in the range
+   * [`srcStart`, `srcStart + srcLength`) into the UnicodeString
+   *  object at offset `start`. `srcChars` is not modified.

    * @param start the offset at which the insertion begins
    * @param srcChars the source for the new characters
    * @param start the offset at which the insertion begins
    * @param srcChars the source for the new characters

-   * @param srcStart the offset into <TT>srcChars</TT> where new characters
+   * @param srcStart the offset into `srcChars` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcChars</TT>
+   * @param srcLength the number of characters in `srcChars`

    * in the insert string
    * @return a reference to this
    * @stable ICU 2.0
    */
   inline UnicodeString& insert(int32_t start,
    * in the insert string
    * @return a reference to this
    * @stable ICU 2.0
    */
   inline UnicodeString& insert(int32_t start,

-            const UChar *srcChars,
+            const char16_t *srcChars,

             int32_t srcStart,
             int32_t srcLength);
 
   /**
             int32_t srcStart,
             int32_t srcLength);
 
   /**

-   * Insert the characters in <TT>srcChars</TT> into the UnicodeString object
-   * at offset <TT>start</TT>. <TT>srcChars</TT> is not modified.
+   * Insert the characters in `srcChars` into the UnicodeString object
+   * at offset `start`. `srcChars` is not modified.

    * @param start the offset where the insertion begins
    * @param srcChars the source for the new characters
    * @param srcLength the number of Unicode characters in srcChars.
    * @param start the offset where the insertion begins
    * @param srcChars the source for the new characters
    * @param srcLength the number of Unicode characters in srcChars.


@@ -2015,23 +2279,23 @@ public:
    * @stable ICU 2.0
    */
   inline UnicodeString& insert(int32_t start,
    * @stable ICU 2.0
    */
   inline UnicodeString& insert(int32_t start,

-            const UChar *srcChars,
+            ConstChar16Ptr srcChars,

             int32_t srcLength);
 
   /**
             int32_t srcLength);
 
   /**

-   * Insert the code unit <TT>srcChar</TT> into the UnicodeString object at
-   * offset <TT>start</TT>.
+   * Insert the code unit `srcChar` into the UnicodeString object at
+   * offset `start`.

    * @param start the offset at which the insertion occurs
    * @param srcChar the code unit to insert
    * @return a reference to this
    * @stable ICU 2.0
    */
   inline UnicodeString& insert(int32_t start,
    * @param start the offset at which the insertion occurs
    * @param srcChar the code unit to insert
    * @return a reference to this
    * @stable ICU 2.0
    */
   inline UnicodeString& insert(int32_t start,

-            UChar srcChar);
+            char16_t srcChar);

 
   /**
 
   /**

-   * Insert the code point <TT>srcChar</TT> into the UnicodeString object at
-   * offset <TT>start</TT>.
+   * Insert the code point `srcChar` into the UnicodeString object at
+   * offset `start`.

    * @param start the offset at which the insertion occurs
    * @param srcChar the code point to insert
    * @return a reference to this
    * @param start the offset at which the insertion occurs
    * @param srcChar the code point to insert
    * @return a reference to this


@@ -2045,22 +2309,22 @@ public:
 
   /**
    * Replace the characters in the range
 
   /**
    * Replace the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the characters in
-   * <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>).
-   * <TT>srcText</TT> is not modified.
+   * [`start`, `start + length`) with the characters in
+   * `srcText` in the range
+   * [`srcStart`, `srcStart + srcLength`).
+   * `srcText` is not modified.

    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace. The character at
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace. The character at

-   * <TT>start + length</TT> is not modified.
+   * `start + length` is not modified.

    * @param srcText the source for the new characters
    * @param srcText the source for the new characters

-   * @param srcStart the offset into <TT>srcText</TT> where new characters
+   * @param srcStart the offset into `srcText` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcText</TT> in
+   * @param srcLength the number of characters in `srcText` in

    * the replace string
    * @return a reference to this
    * @stable ICU 2.0
    */
    * the replace string
    * @return a reference to this
    * @stable ICU 2.0
    */

-  UnicodeString& replace(int32_t start,
+  inline UnicodeString& replace(int32_t start,

              int32_t length,
              const UnicodeString& srcText,
              int32_t srcStart,
              int32_t length,
              const UnicodeString& srcText,
              int32_t srcStart,


@@ -2068,50 +2332,50 @@ public:
 
   /**
    * Replace the characters in the range
 
   /**
    * Replace the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>)
-   * with the characters in <TT>srcText</TT>.  <TT>srcText</TT> is
+   * [`start`, `start + length`)
+   * with the characters in `srcText`.  `srcText` is

    *  not modified.
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace. The character at
    *  not modified.
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace. The character at

-   * <TT>start + length</TT> is not modified.
+   * `start + length` is not modified.

    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcText the source for the new characters
    * @return a reference to this
    * @stable ICU 2.0
    */

-  UnicodeString& replace(int32_t start,
+  inline UnicodeString& replace(int32_t start,

              int32_t length,
              const UnicodeString& srcText);
 
   /**
    * Replace the characters in the range
              int32_t length,
              const UnicodeString& srcText);
 
   /**
    * Replace the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the characters in
-   * <TT>srcChars</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcStart + srcLength</TT>). <TT>srcChars</TT>
+   * [`start`, `start + length`) with the characters in
+   * `srcChars` in the range
+   * [`srcStart`, `srcStart + srcLength`). `srcChars`

    * is not modified.
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace.  The character at
    * is not modified.
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace.  The character at

-   * <TT>start + length</TT> is not modified.
+   * `start + length` is not modified.

    * @param srcChars the source for the new characters
    * @param srcChars the source for the new characters

-   * @param srcStart the offset into <TT>srcChars</TT> where new characters
+   * @param srcStart the offset into `srcChars` where new characters

    * will be obtained
    * will be obtained

-   * @param srcLength the number of characters in <TT>srcChars</TT>
+   * @param srcLength the number of characters in `srcChars`

    * in the replace string
    * @return a reference to this
    * @stable ICU 2.0
    */
    * in the replace string
    * @return a reference to this
    * @stable ICU 2.0
    */

-  UnicodeString& replace(int32_t start,
+  inline UnicodeString& replace(int32_t start,

              int32_t length,
              int32_t length,

-             const UChar *srcChars,
+             const char16_t *srcChars,

              int32_t srcStart,
              int32_t srcLength);
 
   /**
    * Replace the characters in the range
              int32_t srcStart,
              int32_t srcLength);
 
   /**
    * Replace the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the characters in
-   * <TT>srcChars</TT>.  <TT>srcChars</TT> is not modified.
+   * [`start`, `start + length`) with the characters in
+   * `srcChars`.  `srcChars` is not modified.

    * @param start the offset at which the replace operation begins
    * @param length number of characters to replace.  The character at
    * @param start the offset at which the replace operation begins
    * @param length number of characters to replace.  The character at

-   * <TT>start + length</TT> is not modified.
+   * `start + length` is not modified.

    * @param srcChars the source for the new characters
    * @param srcLength the number of Unicode characters in srcChars
    * @return a reference to this
    * @param srcChars the source for the new characters
    * @param srcLength the number of Unicode characters in srcChars
    * @return a reference to this


@@ -2119,42 +2383,40 @@ public:
    */
   inline UnicodeString& replace(int32_t start,
              int32_t length,
    */
   inline UnicodeString& replace(int32_t start,
              int32_t length,

-             const UChar *srcChars,
+             ConstChar16Ptr srcChars,

              int32_t srcLength);
 
   /**
    * Replace the characters in the range
              int32_t srcLength);
 
   /**
    * Replace the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the code unit
-   * <TT>srcChar</TT>.
+   * [`start`, `start + length`) with the code unit
+   * `srcChar`.

    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace.  The character at
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace.  The character at

-   * <TT>start + length</TT> is not modified.
+   * `start + length` is not modified.

    * @param srcChar the new code unit
    * @return a reference to this
    * @stable ICU 2.0
    */
   inline UnicodeString& replace(int32_t start,
              int32_t length,
    * @param srcChar the new code unit
    * @return a reference to this
    * @stable ICU 2.0
    */
   inline UnicodeString& replace(int32_t start,
              int32_t length,

-             UChar srcChar);
+             char16_t srcChar);

 
   /**
    * Replace the characters in the range
 
   /**
    * Replace the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) with the code point
-   * <TT>srcChar</TT>.
+   * [`start`, `start + length`) with the code point
+   * `srcChar`.

    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace.  The character at
    * @param start the offset at which the replace operation begins
    * @param length the number of characters to replace.  The character at

-   * <TT>start + length</TT> is not modified.
+   * `start + length` is not modified.

    * @param srcChar the new code point
    * @return a reference to this
    * @stable ICU 2.0
    */
    * @param srcChar the new code point
    * @return a reference to this
    * @stable ICU 2.0
    */

-  inline UnicodeString& replace(int32_t start,
-             int32_t length,
-             UChar32 srcChar);
+  UnicodeString& replace(int32_t start, int32_t length, UChar32 srcChar);

 
   /**
 
   /**

-   * Replace the characters in the range [<TT>start</TT>, <TT>limit</TT>)
-   * with the characters in <TT>srcText</TT>. <TT>srcText</TT> is not modified.
+   * Replace the characters in the range [`start`, `limit`)
+   * with the characters in `srcText`. `srcText` is not modified.

    * @param start the offset at which the replace operation begins
    * @param limit the offset immediately following the replace range
    * @param srcText the source for the new characters
    * @param start the offset at which the replace operation begins
    * @param limit the offset immediately following the replace range
    * @param srcText the source for the new characters


@@ -2166,16 +2428,16 @@ public:
                 const UnicodeString& srcText);
 
   /**
                 const UnicodeString& srcText);
 
   /**

-   * Replace the characters in the range [<TT>start</TT>, <TT>limit</TT>)
-   * with the characters in <TT>srcText</TT> in the range
-   * [<TT>srcStart</TT>, <TT>srcLimit</TT>). <TT>srcText</TT> is not modified.
+   * Replace the characters in the range [`start`, `limit`)
+   * with the characters in `srcText` in the range
+   * [`srcStart`, `srcLimit`). `srcText` is not modified.

    * @param start the offset at which the replace operation begins
    * @param limit the offset immediately following the replace range
    * @param srcText the source for the new characters
    * @param start the offset at which the replace operation begins
    * @param limit the offset immediately following the replace range
    * @param srcText the source for the new characters

-   * @param srcStart the offset into <TT>srcChars</TT> where new characters
+   * @param srcStart the offset into `srcChars` where new characters

    * will be obtained
    * @param srcLimit the offset immediately following the range to copy
    * will be obtained
    * @param srcLimit the offset immediately following the range to copy

-   * in <TT>srcText</TT>
+   * in `srcText`

    * @return a reference to this
    * @stable ICU 2.0
    */
    * @return a reference to this
    * @stable ICU 2.0
    */


@@ -2187,12 +2449,9 @@ public:
 
   /**
    * Replace a substring of this object with the given text.
 
   /**
    * Replace a substring of this object with the given text.

-   * @param start the beginning index, inclusive; <code>0 <= start
-   * <= limit</code>.
-   * @param limit the ending index, exclusive; <code>start <= limit
-   * <= length()</code>.
-   * @param text the text to replace characters <code>start</code>
-   * to <code>limit - 1</code>
+   * @param start the beginning index, inclusive; `0 <= start <= limit`.
+   * @param limit the ending index, exclusive; `start <= limit <= length()`.
+   * @param text the text to replace characters `start` to `limit - 1`

    * @stable ICU 2.0
    */
   virtual void handleReplaceBetween(int32_t start,
    * @stable ICU 2.0
    */
   virtual void handleReplaceBetween(int32_t start,


@@ -2211,14 +2470,12 @@ public:
    * information.  This method is used to duplicate or reorder substrings.
    * The destination index must not overlap the source range.
    *
    * information.  This method is used to duplicate or reorder substrings.
    * The destination index must not overlap the source range.
    *

-   * @param start the beginning index, inclusive; <code>0 <= start <=
-   * limit</code>.
-   * @param limit the ending index, exclusive; <code>start <= limit <=
-   * length()</code>.
+   * @param start the beginning index, inclusive; `0 <= start <= limit`.
+   * @param limit the ending index, exclusive; `start <= limit <= length()`.

    * @param dest the destination index.  The characters from
    * @param dest the destination index.  The characters from

-   * <code>start..limit-1</code> will be copied to <code>dest</code>.
-   * Implementations of this method may assume that <code>dest <= start ||
-   * dest >= limit</code>.
+   *             `start..limit-1` will be copied to `dest`.
+   * Implementations of this method may assume that `dest <= start ||
+   * dest >= limit`.

    * @stable ICU 2.0
    */
   virtual void copy(int32_t start, int32_t limit, int32_t dest);
    * @stable ICU 2.0
    */
   virtual void copy(int32_t start, int32_t limit, int32_t dest);


@@ -2239,7 +2496,7 @@ public:
   /**
    * Replace all occurrences of characters in oldText with characters
    * in newText
   /**
    * Replace all occurrences of characters in oldText with characters
    * in newText

-   * in the range [<TT>start</TT>, <TT>start + length</TT>).
+   * in the range [`start`, `start + length`).

    * @param start the start of the range in which replace will performed
    * @param length the length of the range in which replace will be performed
    * @param oldText the text containing the search text
    * @param start the start of the range in which replace will performed
    * @param length the length of the range in which replace will be performed
    * @param oldText the text containing the search text


@@ -2254,18 +2511,18 @@ public:
 
   /**
    * Replace all occurrences of characters in oldText in the range
 
   /**
    * Replace all occurrences of characters in oldText in the range

-   * [<TT>oldStart</TT>, <TT>oldStart + oldLength</TT>) with the characters
+   * [`oldStart`, `oldStart + oldLength`) with the characters

    * in newText in the range
    * in newText in the range

-   * [<TT>newStart</TT>, <TT>newStart + newLength</TT>)
-   * in the range [<TT>start</TT>, <TT>start + length</TT>).
+   * [`newStart`, `newStart + newLength`)
+   * in the range [`start`, `start + length`).

    * @param start the start of the range in which replace will performed
    * @param length the length of the range in which replace will be performed
    * @param oldText the text containing the search text
    * @param start the start of the range in which replace will performed
    * @param length the length of the range in which replace will be performed
    * @param oldText the text containing the search text

-   * @param oldStart the start of the search range in <TT>oldText</TT>
-   * @param oldLength the length of the search range in <TT>oldText</TT>
+   * @param oldStart the start of the search range in `oldText`
+   * @param oldLength the length of the search range in `oldText`

    * @param newText the text containing the replacement text
    * @param newText the text containing the replacement text

-   * @param newStart the start of the replacement range in <TT>newText</TT>
-   * @param newLength the length of the replacement range in <TT>newText</TT>
+   * @param newStart the start of the replacement range in `newText`
+   * @param newLength the length of the replacement range in `newText`

    * @return a reference to this
    * @stable ICU 2.0
    */
    * @return a reference to this
    * @stable ICU 2.0
    */


@@ -2290,7 +2547,7 @@ public:
 
   /**
    * Remove the characters in the range
 
   /**
    * Remove the characters in the range

-   * [<TT>start</TT>, <TT>start + length</TT>) from the UnicodeString object.
+   * [`start`, `start + length`) from the UnicodeString object.

    * @param start the offset of the first character to remove
    * @param length the number of characters to remove
    * @return a reference to this
    * @param start the offset of the first character to remove
    * @param length the number of characters to remove
    * @return a reference to this


@@ -2301,7 +2558,7 @@ public:
 
   /**
    * Remove the characters in the range
 
   /**
    * Remove the characters in the range

-   * [<TT>start</TT>, <TT>limit</TT>) from the UnicodeString object.
+   * [`start`, `limit`) from the UnicodeString object.

    * @param start the offset of the first character to remove
    * @param limit the offset immediately following the range to remove
    * @return a reference to this
    * @param start the offset of the first character to remove
    * @param limit the offset immediately following the range to remove
    * @return a reference to this


@@ -2310,11 +2567,21 @@ public:
   inline UnicodeString& removeBetween(int32_t start,
                                       int32_t limit = (int32_t)INT32_MAX);
 
   inline UnicodeString& removeBetween(int32_t start,
                                       int32_t limit = (int32_t)INT32_MAX);
 

+  /**
+   * Retain only the characters in the range
+   * [`start`, `limit`) from the UnicodeString object.
+   * Removes characters before `start` and at and after `limit`.
+   * @param start the offset of the first character to retain
+   * @param limit the offset immediately following the range to retain
+   * @return a reference to this
+   * @stable ICU 4.4
+   */
+  inline UnicodeString &retainBetween(int32_t start, int32_t limit = INT32_MAX);

 
   /* Length operations */
 
   /**
 
   /* Length operations */
 
   /**

-   * Pad the start of this UnicodeString with the character <TT>padChar</TT>.
+   * Pad the start of this UnicodeString with the character `padChar`.

    * If the length of this UnicodeString is less than targetLength,
    * length() - targetLength copies of padChar will be added to the
    * beginning of this UnicodeString.
    * If the length of this UnicodeString is less than targetLength,
    * length() - targetLength copies of padChar will be added to the
    * beginning of this UnicodeString.


@@ -2325,10 +2592,10 @@ public:
    * @stable ICU 2.0
    */
   UBool padLeading(int32_t targetLength,
    * @stable ICU 2.0
    */
   UBool padLeading(int32_t targetLength,

-                    UChar padChar = 0x0020);
+                    char16_t padChar = 0x0020);

 
   /**
 
   /**

-   * Pad the end of this UnicodeString with the character <TT>padChar</TT>.
+   * Pad the end of this UnicodeString with the character `padChar`.

    * If the length of this UnicodeString is less than targetLength,
    * length() - targetLength copies of padChar will be added to the
    * end of this UnicodeString.
    * If the length of this UnicodeString is less than targetLength,
    * length() - targetLength copies of padChar will be added to the
    * end of this UnicodeString.


@@ -2339,10 +2606,10 @@ public:
    * @stable ICU 2.0
    */
   UBool padTrailing(int32_t targetLength,
    * @stable ICU 2.0
    */
   UBool padTrailing(int32_t targetLength,

-                     UChar padChar = 0x0020);
+                     char16_t padChar = 0x0020);

 
   /**
 
   /**

-   * Truncate this UnicodeString to the <TT>targetLength</TT>.
+   * Truncate this UnicodeString to the `targetLength`.

    * @param targetLength the desired length of this UnicodeString.
    * @return TRUE if the text was truncated, FALSE otherwise
    * @stable ICU 2.0
    * @param targetLength the desired length of this UnicodeString.
    * @return TRUE if the text was truncated, FALSE otherwise
    * @stable ICU 2.0


@@ -2367,7 +2634,7 @@ public:
   inline UnicodeString& reverse(void);
 
   /**
   inline UnicodeString& reverse(void);
 
   /**

-   * Reverse the range [<TT>start</TT>, <TT>start + length</TT>) in
+   * Reverse the range [`start`, `start + length`) in

    * this UnicodeString.
    * @param start the start of the range to reverse
    * @param length the number of characters to to reverse
    * this UnicodeString.
    * @param start the start of the range to reverse
    * @param length the number of characters to to reverse


@@ -2428,7 +2695,7 @@ public:
    * The standard titlecase iterator for the root locale implements the
    * algorithm of Unicode TR 21.
    *
    * The standard titlecase iterator for the root locale implements the
    * algorithm of Unicode TR 21.
    *

-   * This function uses only the first() and next() methods of the
+   * This function uses only the setText(), first() and next() methods of the

    * provided break iterator.
    *
    * @param titleIter A break iterator to find the first characters of words
    * provided break iterator.
    *
    * @param titleIter A break iterator to find the first characters of words


@@ -2456,7 +2723,7 @@ public:
    * The standard titlecase iterator for the root locale implements the
    * algorithm of Unicode TR 21.
    *
    * The standard titlecase iterator for the root locale implements the
    * algorithm of Unicode TR 21.
    *

-   * This function uses only the first() and next() methods of the
+   * This function uses only the setText(), first() and next() methods of the

    * provided break iterator.
    *
    * @param titleIter A break iterator to find the first characters of words
    * provided break iterator.
    *
    * @param titleIter A break iterator to find the first characters of words


@@ -2470,13 +2737,48 @@ public:
    */
   UnicodeString &toTitle(BreakIterator *titleIter, const Locale &locale);
 
    */
   UnicodeString &toTitle(BreakIterator *titleIter, const Locale &locale);
 

+  /**
+   * Titlecase this string, with options.
+   *
+   * Casing is locale-dependent and context-sensitive.
+   * Titlecasing uses a break iterator to find the first characters of words
+   * that are to be titlecased. It titlecases those characters and lowercases
+   * all others. (This can be modified with options.)
+   *
+   * The titlecase break iterator can be provided to customize for arbitrary
+   * styles, using rules and dictionaries beyond the standard iterators.
+   * It may be more efficient to always provide an iterator to avoid
+   * opening and closing one for each string.
+   * The standard titlecase iterator for the root locale implements the
+   * algorithm of Unicode TR 21.
+   *
+   * This function uses only the setText(), first() and next() methods of the
+   * provided break iterator.
+   *
+   * @param titleIter A break iterator to find the first characters of words
+   *                  that are to be titlecased.
+   *                  If none is provided (0), then a standard titlecase
+   *                  break iterator is opened.
+   *                  Otherwise the provided iterator is set to the string's text.
+   * @param locale    The locale to consider.
+   * @param options   Options bit set, usually 0. See U_TITLECASE_NO_LOWERCASE,
+   *                  U_TITLECASE_NO_BREAK_ADJUSTMENT, U_TITLECASE_ADJUST_TO_CASED,
+   *                  U_TITLECASE_WHOLE_STRING, U_TITLECASE_SENTENCES.
+   * @param options Options bit set, see ucasemap_open().
+   * @return A reference to this.
+   * @stable ICU 3.8
+   */
+  UnicodeString &toTitle(BreakIterator *titleIter, const Locale &locale, uint32_t options);
+

 #endif
 
   /**
 #endif
 
   /**

-   * Case-fold the characters in this string.
+   * Case-folds the characters in this string.
+   *

    * Case-folding is locale-independent and not context-sensitive,
    * but there is an option for whether to include or exclude mappings for dotted I
    * Case-folding is locale-independent and not context-sensitive,
    * but there is an option for whether to include or exclude mappings for dotted I

-   * and dotless i that are marked with 'I' in CaseFolding.txt.
+   * and dotless i that are marked with 'T' in CaseFolding.txt.
+   *

    * The result may be longer or shorter than the original.
    *
    * @param options Either U_FOLD_CASE_DEFAULT or U_FOLD_CASE_EXCLUDE_SPECIAL_I
    * The result may be longer or shorter than the original.
    *
    * @param options Either U_FOLD_CASE_DEFAULT or U_FOLD_CASE_EXCLUDE_SPECIAL_I


@@ -2491,7 +2793,7 @@ public:
 
   /**
    * Get a read/write pointer to the internal buffer.
 
   /**
    * Get a read/write pointer to the internal buffer.

-   * The buffer is guaranteed to be large enough for at least minCapacity UChars,
+   * The buffer is guaranteed to be large enough for at least minCapacity char16_ts,

    * writable, and is still owned by the UnicodeString object.
    * Calls to getBuffer(minCapacity) must not be nested, and
    * must be matched with calls to releaseBuffer(newLength).
    * writable, and is still owned by the UnicodeString object.
    * Calls to getBuffer(minCapacity) must not be nested, and
    * must be matched with calls to releaseBuffer(newLength).


@@ -2517,22 +2819,22 @@ public:
    *   If the length() was greater than minCapacity, then any contents after minCapacity
    *   may be lost.
    *   The buffer contents is not NUL-terminated by getBuffer().
    *   If the length() was greater than minCapacity, then any contents after minCapacity
    *   may be lost.
    *   The buffer contents is not NUL-terminated by getBuffer().

-   *   If length()<getCapacity() then you can terminate it by writing a NUL
+   *   If length() < getCapacity() then you can terminate it by writing a NUL

    *   at index length().
    * - You must call releaseBuffer(newLength) before and in order to
    *   return to normal UnicodeString operation.
    *
    *   at index length().
    * - You must call releaseBuffer(newLength) before and in order to
    *   return to normal UnicodeString operation.
    *

-   * @param minCapacity the minimum number of UChars that are to be available
+   * @param minCapacity the minimum number of char16_ts that are to be available

    *        in the buffer, starting at the returned pointer;
    *        default to the current string capacity if minCapacity==-1
    * @return a writable pointer to the internal string buffer,
    *        in the buffer, starting at the returned pointer;
    *        default to the current string capacity if minCapacity==-1
    * @return a writable pointer to the internal string buffer,

-   *         or 0 if an error occurs (nested calls, out of memory)
+   *         or nullptr if an error occurs (nested calls, out of memory)

    *
    * @see releaseBuffer
    * @see getTerminatedBuffer()
    * @stable ICU 2.0
    */
    *
    * @see releaseBuffer
    * @see getTerminatedBuffer()
    * @stable ICU 2.0
    */

-  UChar *getBuffer(int32_t minCapacity);
+  char16_t *getBuffer(int32_t minCapacity);

 
   /**
    * Release a read/write buffer on a UnicodeString object with an
 
   /**
    * Release a read/write buffer on a UnicodeString object with an


@@ -2573,20 +2875,20 @@ public:
    *
    * The buffer contents is (probably) not NUL-terminated.
    * You can check if it is with
    *
    * The buffer contents is (probably) not NUL-terminated.
    * You can check if it is with

-   * <code>(s.length()<s.getCapacity() && buffer[s.length()]==0)</code>.
+   * `(s.length() < s.getCapacity() && buffer[s.length()]==0)`.

    * (See getTerminatedBuffer().)
    *
    * The buffer may reside in read-only memory. Its contents must not
    * be modified.
    *
    * @return a read-only pointer to the internal string buffer,
    * (See getTerminatedBuffer().)
    *
    * The buffer may reside in read-only memory. Its contents must not
    * be modified.
    *
    * @return a read-only pointer to the internal string buffer,

-   *         or 0 if the string is empty or bogus
+   *         or nullptr if the string is empty or bogus

    *
    * @see getBuffer(int32_t minCapacity)
    * @see getTerminatedBuffer()
    * @stable ICU 2.0
    */
    *
    * @see getBuffer(int32_t minCapacity)
    * @see getTerminatedBuffer()
    * @stable ICU 2.0
    */

-  inline const UChar *getBuffer() const;
+  inline const char16_t *getBuffer() const;

 
   /**
    * Get a read-only pointer to the internal buffer,
 
   /**
    * Get a read-only pointer to the internal buffer,


@@ -2621,7 +2923,7 @@ public:
    * @see getBuffer()
    * @stable ICU 2.2
    */
    * @see getBuffer()
    * @stable ICU 2.2
    */

-  inline const UChar *getTerminatedBuffer();
+  const char16_t *getTerminatedBuffer();

 
   //========================================
   // Constructors
 
   //========================================
   // Constructors


@@ -2630,11 +2932,11 @@ public:
   /** Construct an empty UnicodeString.
    * @stable ICU 2.0
    */
   /** Construct an empty UnicodeString.
    * @stable ICU 2.0
    */

-  UnicodeString();
+  inline UnicodeString();

 
   /**
 
   /**

-   * Construct a UnicodeString with capacity to hold <TT>capacity</TT> UChars
-   * @param capacity the number of UChars this UnicodeString should hold
+   * Construct a UnicodeString with capacity to hold `capacity` char16_ts
+   * @param capacity the number of char16_ts this UnicodeString should hold

    * before a resize is necessary; if count is greater than 0 and count
    * code points c take up more space than capacity, then capacity is adjusted
    * accordingly.
    * before a resize is necessary; if count is greater than 0 and count
    * code points c take up more space than capacity, then capacity is adjusted
    * accordingly.


@@ -2646,62 +2948,154 @@ public:
   UnicodeString(int32_t capacity, UChar32 c, int32_t count);
 
   /**
   UnicodeString(int32_t capacity, UChar32 c, int32_t count);
 
   /**

-   * Single UChar (code unit) constructor.
+   * Single char16_t (code unit) constructor.
+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_CHAR_EXPLICIT=explicit`
+   * on the compiler command line or similar.

    * @param ch the character to place in the UnicodeString
    * @stable ICU 2.0
    */
    * @param ch the character to place in the UnicodeString
    * @stable ICU 2.0
    */

-  UnicodeString(UChar ch);
+  UNISTR_FROM_CHAR_EXPLICIT UnicodeString(char16_t ch);

 
   /**
    * Single UChar32 (code point) constructor.
 
   /**
    * Single UChar32 (code point) constructor.

+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_CHAR_EXPLICIT=explicit`
+   * on the compiler command line or similar.

    * @param ch the character to place in the UnicodeString
    * @stable ICU 2.0
    */
    * @param ch the character to place in the UnicodeString
    * @stable ICU 2.0
    */

-  UnicodeString(UChar32 ch);
+  UNISTR_FROM_CHAR_EXPLICIT UnicodeString(UChar32 ch);

 
   /**
 
   /**

-   * UChar* constructor.
-   * @param text The characters to place in the UnicodeString.  <TT>text</TT>
+   * char16_t* constructor.
+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
+   * on the compiler command line or similar.
+   * @param text The characters to place in the UnicodeString.  `text`

    * must be NULL (U+0000) terminated.
    * @stable ICU 2.0
    */
    * must be NULL (U+0000) terminated.
    * @stable ICU 2.0
    */

-  UnicodeString(const UChar *text);
+  UNISTR_FROM_STRING_EXPLICIT UnicodeString(const char16_t *text);
+
+#if !U_CHAR16_IS_TYPEDEF
+  /**
+   * uint16_t * constructor.
+   * Delegates to UnicodeString(const char16_t *).
+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
+   * on the compiler command line or similar.
+   * @param text NUL-terminated UTF-16 string
+   * @stable ICU 59
+   */
+  UNISTR_FROM_STRING_EXPLICIT UnicodeString(const uint16_t *text) :
+      UnicodeString(ConstChar16Ptr(text)) {}
+#endif
+
+#if U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN)
+  /**
+   * wchar_t * constructor.
+   * (Only defined if U_SIZEOF_WCHAR_T==2.)
+   * Delegates to UnicodeString(const char16_t *).
+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
+   * on the compiler command line or similar.
+   * @param text NUL-terminated UTF-16 string
+   * @stable ICU 59
+   */
+  UNISTR_FROM_STRING_EXPLICIT UnicodeString(const wchar_t *text) :
+      UnicodeString(ConstChar16Ptr(text)) {}
+#endif

 
   /**
 
   /**

-   * UChar* constructor.
+   * nullptr_t constructor.
+   * Effectively the same as the default constructor, makes an empty string object.
+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
+   * on the compiler command line or similar.
+   * @param text nullptr
+   * @stable ICU 59
+   */
+  UNISTR_FROM_STRING_EXPLICIT inline UnicodeString(const std::nullptr_t text);
+
+  /**
+   * char16_t* constructor.

    * @param text The characters to place in the UnicodeString.
    * @param text The characters to place in the UnicodeString.

-   * @param textLength The number of Unicode characters in <TT>text</TT>
+   * @param textLength The number of Unicode characters in `text`

    * to copy.
    * @stable ICU 2.0
    */
    * to copy.
    * @stable ICU 2.0
    */

-  UnicodeString(const UChar *text,
+  UnicodeString(const char16_t *text,

         int32_t textLength);
 
         int32_t textLength);
 

+#if !U_CHAR16_IS_TYPEDEF
+  /**
+   * uint16_t * constructor.
+   * Delegates to UnicodeString(const char16_t *, int32_t).
+   * @param text UTF-16 string
+   * @param length string length
+   * @stable ICU 59
+   */
+  UnicodeString(const uint16_t *text, int32_t length) :
+      UnicodeString(ConstChar16Ptr(text), length) {}
+#endif
+
+#if U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN)
+  /**
+   * wchar_t * constructor.
+   * (Only defined if U_SIZEOF_WCHAR_T==2.)
+   * Delegates to UnicodeString(const char16_t *, int32_t).
+   * @param text NUL-terminated UTF-16 string
+   * @param length string length
+   * @stable ICU 59
+   */
+  UnicodeString(const wchar_t *text, int32_t length) :
+      UnicodeString(ConstChar16Ptr(text), length) {}
+#endif
+

   /**
   /**

-   * Readonly-aliasing UChar* constructor.
+   * nullptr_t constructor.
+   * Effectively the same as the default constructor, makes an empty string object.
+   * @param text nullptr
+   * @param length ignored
+   * @stable ICU 59
+   */
+  inline UnicodeString(const std::nullptr_t text, int32_t length);
+
+  /**
+   * Readonly-aliasing char16_t* constructor.

    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has copy-on-write semantics:
    * When the string is modified, then the buffer is first copied into
    * newly allocated memory.
    * The aliased buffer is never modified.
    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has copy-on-write semantics:
    * When the string is modified, then the buffer is first copied into
    * newly allocated memory.
    * The aliased buffer is never modified.

-   * In an assignment to another UnicodeString, the text will be aliased again,
+   *
+   * In an assignment to another UnicodeString, when using the copy constructor
+   * or the assignment operator, the text will be copied.
+   * When using fastCopyFrom(), the text will be aliased again,

    * so that both strings then alias the same readonly-text.
    *
    * so that both strings then alias the same readonly-text.
    *

-   * @param isTerminated specifies if <code>text</code> is <code>NUL</code>-terminated.
-   *                     This must be true if <code>textLength==-1</code>.
+   * @param isTerminated specifies if `text` is `NUL`-terminated.
+   *                     This must be true if `textLength==-1`.

    * @param text The characters to alias for the UnicodeString.
    * @param text The characters to alias for the UnicodeString.

-   * @param textLength The number of Unicode characters in <code>text</code> to alias.
+   * @param textLength The number of Unicode characters in `text` to alias.

    *                   If -1, then this constructor will determine the length
    *                   If -1, then this constructor will determine the length

-   *                   by calling <code>u_strlen()</code>.
+   *                   by calling `u_strlen()`.

    * @stable ICU 2.0
    */
   UnicodeString(UBool isTerminated,
    * @stable ICU 2.0
    */
   UnicodeString(UBool isTerminated,

-                const UChar *text,
+                ConstChar16Ptr text,

                 int32_t textLength);
 
   /**
                 int32_t textLength);
 
   /**

-   * Writable-aliasing UChar* constructor.
+   * Writable-aliasing char16_t* constructor.

    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has write-through semantics:
    * The text will be used for the UnicodeString object, but
    * it will not be released when the UnicodeString is destroyed.
    * This has write-through semantics:


@@ -2710,26 +3104,98 @@ public:
    * a new buffer will be allocated and the contents copied as with regularly
    * constructed strings.
    * In an assignment to another UnicodeString, the buffer will be copied.
    * a new buffer will be allocated and the contents copied as with regularly
    * constructed strings.
    * In an assignment to another UnicodeString, the buffer will be copied.

-   * The extract(UChar *dst) function detects whether the dst pointer is the same
+   * The extract(Char16Ptr dst) function detects whether the dst pointer is the same

    * as the string buffer itself and will in this case not copy the contents.
    *
    * @param buffer The characters to alias for the UnicodeString.
    * as the string buffer itself and will in this case not copy the contents.
    *
    * @param buffer The characters to alias for the UnicodeString.

-   * @param buffLength The number of Unicode characters in <code>buffer</code> to alias.
-   * @param buffCapacity The size of <code>buffer</code> in UChars.
+   * @param buffLength The number of Unicode characters in `buffer` to alias.
+   * @param buffCapacity The size of `buffer` in char16_ts.

    * @stable ICU 2.0
    */
    * @stable ICU 2.0
    */

-  UnicodeString(UChar *buffer, int32_t buffLength, int32_t buffCapacity);
+  UnicodeString(char16_t *buffer, int32_t buffLength, int32_t buffCapacity);
+
+#if !U_CHAR16_IS_TYPEDEF
+  /**
+   * Writable-aliasing uint16_t * constructor.
+   * Delegates to UnicodeString(const char16_t *, int32_t, int32_t).
+   * @param buffer writable buffer of/for UTF-16 text
+   * @param buffLength length of the current buffer contents
+   * @param buffCapacity buffer capacity
+   * @stable ICU 59
+   */
+  UnicodeString(uint16_t *buffer, int32_t buffLength, int32_t buffCapacity) :
+      UnicodeString(Char16Ptr(buffer), buffLength, buffCapacity) {}
+#endif
+
+#if U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN)
+  /**
+   * Writable-aliasing wchar_t * constructor.
+   * (Only defined if U_SIZEOF_WCHAR_T==2.)
+   * Delegates to UnicodeString(const char16_t *, int32_t, int32_t).
+   * @param buffer writable buffer of/for UTF-16 text
+   * @param buffLength length of the current buffer contents
+   * @param buffCapacity buffer capacity
+   * @stable ICU 59
+   */
+  UnicodeString(wchar_t *buffer, int32_t buffLength, int32_t buffCapacity) :
+      UnicodeString(Char16Ptr(buffer), buffLength, buffCapacity) {}
+#endif
+
+  /**
+   * Writable-aliasing nullptr_t constructor.
+   * Effectively the same as the default constructor, makes an empty string object.
+   * @param buffer nullptr
+   * @param buffLength ignored
+   * @param buffCapacity ignored
+   * @stable ICU 59
+   */
+  inline UnicodeString(std::nullptr_t buffer, int32_t buffLength, int32_t buffCapacity);
+
+#if U_CHARSET_IS_UTF8 || !UCONFIG_NO_CONVERSION
+
+  /**
+   * char* constructor.
+   * Uses the default converter (and thus depends on the ICU conversion code)
+   * unless U_CHARSET_IS_UTF8 is set to 1.
+   *
+   * For ASCII (really "invariant character") strings it is more efficient to use
+   * the constructor that takes a US_INV (for its enum EInvariant).
+   * For ASCII (invariant-character) string literals, see UNICODE_STRING and
+   * UNICODE_STRING_SIMPLE.
+   *
+   * It is recommended to mark this constructor "explicit" by
+   * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
+   * on the compiler command line or similar.
+   * @param codepageData an array of bytes, null-terminated,
+   *                     in the platform's default codepage.
+   * @stable ICU 2.0
+   * @see UNICODE_STRING
+   * @see UNICODE_STRING_SIMPLE
+   */
+  UNISTR_FROM_STRING_EXPLICIT UnicodeString(const char *codepageData);
+
+  /**
+   * char* constructor.
+   * Uses the default converter (and thus depends on the ICU conversion code)
+   * unless U_CHARSET_IS_UTF8 is set to 1.
+   * @param codepageData an array of bytes in the platform's default codepage.
+   * @param dataLength The number of bytes in `codepageData`.
+   * @stable ICU 2.0
+   */
+  UnicodeString(const char *codepageData, int32_t dataLength);
+
+#endif

 
 #if !UCONFIG_NO_CONVERSION
 
   /**
    * char* constructor.
    * @param codepageData an array of bytes, null-terminated
 
 #if !UCONFIG_NO_CONVERSION
 
   /**
    * char* constructor.
    * @param codepageData an array of bytes, null-terminated

-   * @param codepage the encoding of <TT>codepageData</TT>.  The special
-   * value 0 for <TT>codepage</TT> indicates that the text is in the
+   * @param codepage the encoding of `codepageData`.  The special
+   * value 0 for `codepage` indicates that the text is in the

    * platform's default codepage.
    *
    * platform's default codepage.
    *

-   * If <code>codepage</code> is an empty string (<code>""</code>),
+   * If `codepage` is an empty string (`""`),

    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    * Recommendation: For invariant-character strings use the constructor
    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    * Recommendation: For invariant-character strings use the constructor


@@ -2739,17 +3205,16 @@ public:
    *
    * @stable ICU 2.0
    */
    *
    * @stable ICU 2.0
    */

-  UnicodeString(const char *codepageData,
-        const char *codepage = 0);
+  UnicodeString(const char *codepageData, const char *codepage);

 
   /**
    * char* constructor.
    * @param codepageData an array of bytes.
 
   /**
    * char* constructor.
    * @param codepageData an array of bytes.

-   * @param dataLength The number of bytes in <TT>codepageData</TT>.
-   * @param codepage the encoding of <TT>codepageData</TT>.  The special
-   * value 0 for <TT>codepage</TT> indicates that the text is in the
+   * @param dataLength The number of bytes in `codepageData`.
+   * @param codepage the encoding of `codepageData`.  The special
+   * value 0 for `codepage` indicates that the text is in the

    * platform's default codepage.
    * platform's default codepage.

-   * If <code>codepage</code> is an empty string (<code>""</code>),
+   * If `codepage` is an empty string (`""`),

    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    * Recommendation: For invariant-character strings use the constructor
    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    * Recommendation: For invariant-character strings use the constructor


@@ -2759,9 +3224,7 @@ public:
    *
    * @stable ICU 2.0
    */
    *
    * @stable ICU 2.0
    */

-  UnicodeString(const char *codepageData,
-        int32_t dataLength,
-        const char *codepage = 0);
+  UnicodeString(const char *codepageData, int32_t dataLength, const char *codepage);

 
   /**
    * char * / UConverter constructor.
 
   /**
    * char * / UConverter constructor.


@@ -2802,33 +3265,51 @@ public:
    *
    * For example:
    * \code
    *
    * For example:
    * \code

-   * void fn(const char *s) {
-   *   UnicodeString ustr(s, -1, US_INV);
-   *   // use ustr ...
-   * }
+   *     void fn(const char *s) {
+   *       UnicodeString ustr(s, -1, US_INV);
+   *       // use ustr ...
+   *     }

    * \endcode
    * \endcode

-   *

    * @param src String using only invariant characters.
    * @param length Length of src, or -1 if NUL-terminated.
    * @param inv Signature-distinguishing paramater, use US_INV.
    *
    * @see US_INV
    * @param src String using only invariant characters.
    * @param length Length of src, or -1 if NUL-terminated.
    * @param inv Signature-distinguishing paramater, use US_INV.
    *
    * @see US_INV

-   * @draft ICU 3.2
+   * @stable ICU 3.2

    */
   UnicodeString(const char *src, int32_t length, enum EInvariant inv);
 
 
   /**
    * Copy constructor.
    */
   UnicodeString(const char *src, int32_t length, enum EInvariant inv);
 
 
   /**
    * Copy constructor.

+   *
+   * Starting with ICU 2.4, the assignment operator and the copy constructor
+   * allocate a new buffer and copy the buffer contents even for readonly aliases.
+   * By contrast, the fastCopyFrom() function implements the old,
+   * more efficient but less safe behavior
+   * of making this string also a readonly alias to the same buffer.
+   *
+   * If the source object has an "open" buffer from getBuffer(minCapacity),
+   * then the copy is an empty string.
+   *

    * @param that The UnicodeString object to copy.
    * @stable ICU 2.0
    * @param that The UnicodeString object to copy.
    * @stable ICU 2.0

+   * @see fastCopyFrom

    */
   UnicodeString(const UnicodeString& that);
 
    */
   UnicodeString(const UnicodeString& that);
 

+  /**
+   * Move constructor; might leave src in bogus state.
+   * This string will have the same contents and state that the source string had.
+   * @param src source string
+   * @stable ICU 56
+   */
+  UnicodeString(UnicodeString &&src) U_NOEXCEPT;
+

   /**
    * 'Substring' constructor from tail of source string.
    * @param src The UnicodeString object to copy.
   /**
    * 'Substring' constructor from tail of source string.
    * @param src The UnicodeString object to copy.

-   * @param srcStart The offset into <tt>src</tt> at which to start copying.
+   * @param srcStart The offset into `src` at which to start copying.

    * @stable ICU 2.2
    */
   UnicodeString(const UnicodeString& src, int32_t srcStart);
    * @stable ICU 2.2
    */
   UnicodeString(const UnicodeString& src, int32_t srcStart);


@@ -2836,8 +3317,8 @@ public:
   /**
    * 'Substring' constructor from subrange of source string.
    * @param src The UnicodeString object to copy.
   /**
    * 'Substring' constructor from subrange of source string.
    * @param src The UnicodeString object to copy.

-   * @param srcStart The offset into <tt>src</tt> at which to start copying.
-   * @param srcLength The number of characters from <tt>src</tt> to copy.
+   * @param srcStart The offset into `src` at which to start copying.
+   * @param srcLength The number of characters from `src` to copy.

    * @stable ICU 2.2
    */
   UnicodeString(const UnicodeString& src, int32_t srcStart, int32_t srcLength);
    * @stable ICU 2.2
    */
   UnicodeString(const UnicodeString& src, int32_t srcStart, int32_t srcLength);


@@ -2865,6 +3346,33 @@ public:
    */
   virtual ~UnicodeString();
 
    */
   virtual ~UnicodeString();
 

+  /**
+   * Create a UnicodeString from a UTF-8 string.
+   * Illegal input is replaced with U+FFFD. Otherwise, errors result in a bogus string.
+   * Calls u_strFromUTF8WithSub().
+   *
+   * @param utf8 UTF-8 input string.
+   *             Note that a StringPiece can be implicitly constructed
+   *             from a std::string or a NUL-terminated const char * string.
+   * @return A UnicodeString with equivalent UTF-16 contents.
+   * @see toUTF8
+   * @see toUTF8String
+   * @stable ICU 4.2
+   */
+  static UnicodeString fromUTF8(StringPiece utf8);
+
+  /**
+   * Create a UnicodeString from a UTF-32 string.
+   * Illegal input is replaced with U+FFFD. Otherwise, errors result in a bogus string.
+   * Calls u_strFromUTF32WithSub().
+   *
+   * @param utf32 UTF-32 input string. Must not be NULL.
+   * @param length Length of the input string, or -1 if NUL-terminated.
+   * @return A UnicodeString with equivalent UTF-16 contents.
+   * @see toUTF32
+   * @stable ICU 4.2
+   */
+  static UnicodeString fromUTF32(const UChar32 *utf32, int32_t length);

 
   /* Miscellaneous operations */
 
 
   /* Miscellaneous operations */
 


@@ -2909,7 +3417,7 @@ public:
    * character.  See unescape() for a listing of the recognized escape
    * sequences.  The character at offset-1 is assumed (without
    * checking) to be a backslash.  If the escape sequence is
    * character.  See unescape() for a listing of the recognized escape
    * sequences.  The character at offset-1 is assumed (without
    * checking) to be a backslash.  If the escape sequence is

-   * ill-formed, or the offset is out of range, (UChar32)0xFFFFFFFF is
+   * ill-formed, or the offset is out of range, U_SENTINEL=-1 is

    * returned.
    *
    * @param offset an input output parameter.  On input, it is the
    * returned.
    *
    * @param offset an input output parameter.  On input, it is the


@@ -2917,7 +3425,7 @@ public:
    * after the initial backslash.  On output, it is advanced after the
    * last character parsed.  On error, it is not advanced at all.
    * @return the character represented by the escape sequence at
    * after the initial backslash.  On output, it is advanced after the
    * last character parsed.  On error, it is not advanced at all.
    * @return the character represented by the escape sequence at

-   * offset, or (UChar32)0xFFFFFFFF on error.
+   * offset, or U_SENTINEL=-1 on error.

    * @see UnicodeString#unescape()
    * @see u_unescape()
    * @see u_unescapeAt()
    * @see UnicodeString#unescape()
    * @see u_unescape()
    * @see u_unescapeAt()


@@ -2955,7 +3463,7 @@ protected:
    * UnicodeString::charAt() to be inline again (see jitterbug 709).
    * @stable ICU 2.4
    */
    * UnicodeString::charAt() to be inline again (see jitterbug 709).
    * @stable ICU 2.4
    */

-  virtual UChar getCharAt(int32_t offset) const;
+  virtual char16_t getCharAt(int32_t offset) const;

 
   /**
    * The change in Replaceable to use virtual getChar32At() allows
 
   /**
    * The change in Replaceable to use virtual getChar32At() allows


@@ -2965,6 +3473,22 @@ protected:
   virtual UChar32 getChar32At(int32_t offset) const;
 
 private:
   virtual UChar32 getChar32At(int32_t offset) const;
 
 private:

+  // For char* constructors. Could be made public.
+  UnicodeString &setToUTF8(StringPiece utf8);
+  // For extract(char*).
+  // We could make a toUTF8(target, capacity, errorCode) public but not
+  // this version: New API will be cleaner if we make callers create substrings
+  // rather than having start+length on every method,
+  // and it should take a UErrorCode&.
+  int32_t
+  toUTF8(int32_t start, int32_t len,
+         char *target, int32_t capacity) const;
+
+  /**
+   * Internal string contents comparison, called by operator==.
+   * Requires: this & text not bogus and have same lengths.
+   */
+  UBool doEquals(const UnicodeString &text, int32_t len) const;

 
   inline int8_t
   doCompare(int32_t start,
 
   inline int8_t
   doCompare(int32_t start,


@@ -2975,7 +3499,7 @@ private:
 
   int8_t doCompare(int32_t start,
            int32_t length,
 
   int8_t doCompare(int32_t start,
            int32_t length,

-           const UChar *srcChars,
+           const char16_t *srcChars,

            int32_t srcStart,
            int32_t srcLength) const;
 
            int32_t srcStart,
            int32_t srcLength) const;
 


@@ -2988,7 +3512,7 @@ private:
 
   int8_t doCompareCodePointOrder(int32_t start,
                                  int32_t length,
 
   int8_t doCompareCodePointOrder(int32_t start,
                                  int32_t length,

-                                 const UChar *srcChars,
+                                 const char16_t *srcChars,

                                  int32_t srcStart,
                                  int32_t srcLength) const;
 
                                  int32_t srcStart,
                                  int32_t srcLength) const;
 


@@ -3003,12 +3527,12 @@ private:
   int8_t
   doCaseCompare(int32_t start,
                 int32_t length,
   int8_t
   doCaseCompare(int32_t start,
                 int32_t length,

-                const UChar *srcChars,
+                const char16_t *srcChars,

                 int32_t srcStart,
                 int32_t srcLength,
                 uint32_t options) const;
 
                 int32_t srcStart,
                 int32_t srcLength,
                 uint32_t options) const;
 

-  int32_t doIndexOf(UChar c,
+  int32_t doIndexOf(char16_t c,

             int32_t start,
             int32_t length) const;
 
             int32_t start,
             int32_t length) const;
 


@@ -3016,7 +3540,7 @@ private:
                         int32_t start,
                         int32_t length) const;
 
                         int32_t start,
                         int32_t length) const;
 

-  int32_t doLastIndexOf(UChar c,
+  int32_t doLastIndexOf(char16_t c,

                 int32_t start,
                 int32_t length) const;
 
                 int32_t start,
                 int32_t length) const;
 


@@ -3026,14 +3550,14 @@ private:
 
   void doExtract(int32_t start,
          int32_t length,
 
   void doExtract(int32_t start,
          int32_t length,

-         UChar *dst,
+         char16_t *dst,

          int32_t dstStart) const;
 
   inline void doExtract(int32_t start,
          int32_t length,
          UnicodeString& target) const;
 
          int32_t dstStart) const;
 
   inline void doExtract(int32_t start,
          int32_t length,
          UnicodeString& target) const;
 

-  inline UChar doCharAt(int32_t offset)  const;
+  inline char16_t doCharAt(int32_t offset)  const;

 
   UnicodeString& doReplace(int32_t start,
                int32_t length,
 
   UnicodeString& doReplace(int32_t start,
                int32_t length,


@@ -3043,10 +3567,13 @@ private:
 
   UnicodeString& doReplace(int32_t start,
                int32_t length,
 
   UnicodeString& doReplace(int32_t start,
                int32_t length,

-               const UChar *srcChars,
+               const char16_t *srcChars,

                int32_t srcStart,
                int32_t srcLength);
 
                int32_t srcStart,
                int32_t srcLength);
 

+  UnicodeString& doAppend(const UnicodeString& src, int32_t srcStart, int32_t srcLength);
+  UnicodeString& doAppend(const char16_t *srcChars, int32_t srcStart, int32_t srcLength);
+

   UnicodeString& doReverse(int32_t start,
                int32_t length);
 
   UnicodeString& doReverse(int32_t start,
                int32_t length);
 


@@ -3054,12 +3581,31 @@ private:
   int32_t doHashCode(void) const;
 
   // get pointer to start of array
   int32_t doHashCode(void) const;
 
   // get pointer to start of array

-  inline UChar* getArrayStart(void);
-  inline const UChar* getArrayStart(void) const;
+  // these do not check for kOpenGetBuffer, unlike the public getBuffer() function
+  inline char16_t* getArrayStart(void);
+  inline const char16_t* getArrayStart(void) const;
+
+  inline UBool hasShortLength() const;
+  inline int32_t getShortLength() const;
+
+  // A UnicodeString object (not necessarily its current buffer)
+  // is writable unless it isBogus() or it has an "open" getBuffer(minCapacity).
+  inline UBool isWritable() const;
+
+  // Is the current buffer writable?
+  inline UBool isBufferWritable() const;

 
 

-  // allocate the array; result may be fStackBuffer
+  // None of the following does releaseArray().
+  inline void setZeroLength();
+  inline void setShortLength(int32_t len);
+  inline void setLength(int32_t len);
+  inline void setToEmpty();
+  inline void setArray(char16_t *array, int32_t len, int32_t capacity); // sets length but not flags
+
+  // allocate the array; result may be the stack buffer

   // sets refCount to 1 if appropriate
   // sets refCount to 1 if appropriate

-  // sets fArray, fCapacity, and fFlags
+  // sets fArray, fCapacity, and flags
+  // sets length to 0

   // returns boolean for success or failure
   UBool allocate(int32_t capacity);
 
   // returns boolean for success or failure
   UBool allocate(int32_t capacity);
 


@@ -3072,6 +3618,9 @@ private:
   // implements assigment operator, copy constructor, and fastCopyFrom()
   UnicodeString &copyFrom(const UnicodeString &src, UBool fastCopy=FALSE);
 
   // implements assigment operator, copy constructor, and fastCopyFrom()
   UnicodeString &copyFrom(const UnicodeString &src, UBool fastCopy=FALSE);
 

+  // Copies just the fields without memory management.
+  void copyFieldsFrom(UnicodeString &src, UBool setSrcToBogus) U_NOEXCEPT;
+

   // Pin start and limit to acceptable values.
   inline void pinIndex(int32_t& start) const;
   inline void pinIndices(int32_t& start,
   // Pin start and limit to acceptable values.
   inline void pinIndex(int32_t& start) const;
   inline void pinIndices(int32_t& start,


@@ -3089,9 +3638,9 @@ private:
    * Real constructor for converting from codepage data.
    * It assumes that it is called with !fRefCounted.
    *
    * Real constructor for converting from codepage data.
    * It assumes that it is called with !fRefCounted.
    *

-   * If <code>codepage==0</code>, then the default converter
+   * If `codepage==0`, then the default converter

    * is used for the platform encoding.
    * is used for the platform encoding.

-   * If <code>codepage</code> is an empty string (<code>""</code>),
+   * If `codepage` is an empty string (`""`),

    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    */
    * then a simple conversion is performed on the codepage-invariant
    * subset ("invariant characters") of the platform encoding. See utypes.h.
    */


@@ -3128,12 +3677,17 @@ private:
                             int32_t **pBufferToDelete = 0,
                             UBool forceClone = FALSE);
 
                             int32_t **pBufferToDelete = 0,
                             UBool forceClone = FALSE);
 

-  // common function for case mappings
+  /**
+   * Common function for UnicodeString case mappings.
+   * The stringCaseMapper has the same type UStringCaseMapper
+   * as in ustr_imp.h for ustrcase_map().
+   */

   UnicodeString &
   UnicodeString &

-  caseMap(BreakIterator *titleIter,
-          const char *locale,
-          uint32_t options,
-          int32_t toWhichCase);
+  caseMap(int32_t caseLocale, uint32_t options,
+#if !UCONFIG_NO_BREAK_ITERATION
+          BreakIterator *iter,
+#endif
+          UStringCaseMapper *stringCaseMapper);

 
   // ref counting
   void addRef(void);
 
   // ref counting
   void addRef(void);


@@ -3142,19 +3696,29 @@ private:
 
   // constants
   enum {
 
   // constants
   enum {

-    US_STACKBUF_SIZE=7, // Size of stack buffer for small strings
-    kInvalidUChar=0xffff, // invalid UChar index
-    kGrowSize=128, // grow size for this buffer
+    /**
+     * Size of stack buffer for short strings.
+     * Must be at least U16_MAX_LENGTH for the single-code point constructor to work.
+     * @see UNISTR_OBJECT_SIZE
+     */
+    US_STACKBUF_SIZE=(int32_t)(UNISTR_OBJECT_SIZE-sizeof(void *)-2)/U_SIZEOF_UCHAR,
+    kInvalidUChar=0xffff, // U+FFFF returned by charAt(invalid index)

     kInvalidHashCode=0, // invalid hash code
     kEmptyHashCode=1, // hash code for empty string
 
     kInvalidHashCode=0, // invalid hash code
     kEmptyHashCode=1, // hash code for empty string
 

-    // bit flag values for fFlags
+    // bit flag values for fLengthAndFlags

     kIsBogus=1,         // this string is bogus, i.e., not valid or NULL
     kIsBogus=1,         // this string is bogus, i.e., not valid or NULL

-    kUsingStackBuffer=2,// fArray==fStackBuffer
+    kUsingStackBuffer=2,// using fUnion.fStackFields instead of fUnion.fFields

     kRefCounted=4,      // there is a refCount field before the characters in fArray
     kBufferIsReadonly=8,// do not write to this buffer
     kOpenGetBuffer=16,  // getBuffer(minCapacity) was called (is "open"),
                         // and releaseBuffer(newLength) must be called
     kRefCounted=4,      // there is a refCount field before the characters in fArray
     kBufferIsReadonly=8,// do not write to this buffer
     kOpenGetBuffer=16,  // getBuffer(minCapacity) was called (is "open"),
                         // and releaseBuffer(newLength) must be called

+    kAllStorageFlags=0x1f,
+
+    kLengthShift=5,     // remaining 11 bits for non-negative short length, or negative if long
+    kLength1=1<<kLengthShift,
+    kMaxShortLength=0x3ff,  // max non-negative short length (leaves top bit 0)
+    kLengthIsLarge=0xffe0,  // short length < 0, real length is in fUnion.fFields.fLength

 
     // combined values for convenience
     kShortString=kUsingStackBuffer,
 
     // combined values for convenience
     kShortString=kUsingStackBuffer,


@@ -3163,8 +3727,10 @@ private:
     kWritableAlias=0
   };
 
     kWritableAlias=0
   };
 

-  friend class StringCharacterIterator;
-  friend class StringThreadTest;
+  friend class UnicodeStringAppendable;
+
+  union StackBufferOrFields;        // forward declaration necessary before friend declaration
+  friend union StackBufferOrFields; // make US_STACKBUF_SIZE visible inside fUnion

 
   /*
    * The following are all the class fields that are stored
 
   /*
    * The following are all the class fields that are stored


@@ -3172,18 +3738,57 @@ private:
    * Note that UnicodeString has virtual functions,
    * therefore there is an implicit vtable pointer
    * as the first real field.
    * Note that UnicodeString has virtual functions,
    * therefore there is an implicit vtable pointer
    * as the first real field.

-   * The fields should be aligned such that no padding is
-   * necessary, mostly by having larger types first.
+   * The fields should be aligned such that no padding is necessary.

    * On 32-bit machines, the size should be 32 bytes,
    * on 64-bit machines (8-byte pointers), it should be 40 bytes.
    * On 32-bit machines, the size should be 32 bytes,
    * on 64-bit machines (8-byte pointers), it should be 40 bytes.

+   *
+   * We use a hack to achieve this.
+   *
+   * With at least some compilers, each of the following is forced to
+   * a multiple of sizeof(pointer) [the largest field base unit here is a data pointer],
+   * rounded up with additional padding if the fields do not already fit that requirement:
+   * - sizeof(class UnicodeString)
+   * - offsetof(UnicodeString, fUnion)
+   * - sizeof(fUnion)
+   * - sizeof(fStackFields)
+   *
+   * We optimize for the longest possible internal buffer for short strings.
+   * fUnion.fStackFields begins with 2 bytes for storage flags
+   * and the length of relatively short strings,
+   * followed by the buffer for short string contents.
+   * There is no padding inside fStackFields.
+   *
+   * Heap-allocated and aliased strings use fUnion.fFields.
+   * Both fStackFields and fFields must begin with the same fields for flags and short length,
+   * that is, those must have the same memory offsets inside the object,
+   * because the flags must be inspected in order to decide which half of fUnion is being used.
+   * We assume that the compiler does not reorder the fields.
+   *
+   * (Padding at the end of fFields is ok:
+   * As long as it is no larger than fStackFields, it is not wasted space.)
+   *
+   * For some of the history of the UnicodeString class fields layout, see
+   * - ICU ticket #11551 "longer UnicodeString contents in stack buffer"
+   * - ICU ticket #11336 "UnicodeString: recombine stack buffer arrays"
+   * - ICU ticket #8322 "why is sizeof(UnicodeString)==48?"

    */
   // (implicit) *vtable;
    */
   // (implicit) *vtable;

-  int32_t   fLength;        // number of characters in fArray
-  int32_t   fCapacity;      // sizeof fArray
-  UChar     *fArray;        // the Unicode data
-  uint16_t  fFlags;         // bit flags: see constants above
-  UChar     fStackBuffer [ US_STACKBUF_SIZE ]; // buffer for small strings
-
+  union StackBufferOrFields {
+    // fStackFields is used iff (fLengthAndFlags&kUsingStackBuffer) else fFields is used.
+    // Each struct of the union must begin with fLengthAndFlags.
+    struct {
+      int16_t fLengthAndFlags;          // bit fields: see constants above
+      char16_t fBuffer[US_STACKBUF_SIZE];  // buffer for short strings
+    } fStackFields;
+    struct {
+      int16_t fLengthAndFlags;          // bit fields: see constants above
+      int32_t fLength;    // number of characters in fArray if >127; else undefined
+      int32_t fCapacity;  // capacity of fArray (in char16_ts)
+      // array pointer last to minimize padding for machines with P128 data model
+      // or pointer sizes that are not a power of 2
+      char16_t   *fArray;    // the Unicode data
+    } fFields;
+  } fUnion;

 };
 
 /**
 };
 
 /**


@@ -3192,37 +3797,11 @@ private:
  * @param s1 The first string to be copied to the new one.
  * @param s2 The second string to be copied to the new one, after s1.
  * @return UnicodeString(s1).append(s2)
  * @param s1 The first string to be copied to the new one.
  * @param s2 The second string to be copied to the new one, after s1.
  * @return UnicodeString(s1).append(s2)

- * @draft ICU 2.8
+ * @stable ICU 2.8

  */
 U_COMMON_API UnicodeString U_EXPORT2
 operator+ (const UnicodeString &s1, const UnicodeString &s2);
 
  */
 U_COMMON_API UnicodeString U_EXPORT2
 operator+ (const UnicodeString &s1, const UnicodeString &s2);
 

-U_NAMESPACE_END
-
-// inline implementations -------------------------------------------------- ***
-
-//========================================
-// Array copying
-//========================================
-/**
- * Copy an array of UnicodeString OBJECTS (not pointers).
- * @internal
- */
-inline void
-uprv_arrayCopy(const U_NAMESPACE_QUALIFIER UnicodeString *src, U_NAMESPACE_QUALIFIER UnicodeString *dst, int32_t count)
-{ while(count-- > 0) *dst++ = *src++; }
-
-/**
- * Copy an array of UnicodeString OBJECTS (not pointers).
- * @internal
- */
-inline void
-uprv_arrayCopy(const U_NAMESPACE_QUALIFIER UnicodeString *src, int32_t srcStart,
-        U_NAMESPACE_QUALIFIER UnicodeString *dst, int32_t dstStart, int32_t count)
-{ uprv_arrayCopy(src+srcStart, dst+dstStart, count); }
-
-U_NAMESPACE_BEGIN
-

 //========================================
 // Inline members
 //========================================
 //========================================
 // Inline members
 //========================================


@@ -3237,8 +3816,8 @@ UnicodeString::pinIndex(int32_t& start) const
   // pin index
   if(start < 0) {
     start = 0;
   // pin index
   if(start < 0) {
     start = 0;

-  } else if(start > fLength) {
-    start = fLength;
+  } else if(start > length()) {
+    start = length();

   }
 }
 
   }
 }
 


@@ -3247,36 +3826,77 @@ UnicodeString::pinIndices(int32_t& start,
                           int32_t& _length) const
 {
   // pin indices
                           int32_t& _length) const
 {
   // pin indices

+  int32_t len = length();

   if(start < 0) {
     start = 0;
   if(start < 0) {
     start = 0;

-  } else if(start > fLength) {
-    start = fLength;
+  } else if(start > len) {
+    start = len;

   }
   if(_length < 0) {
     _length = 0;
   }
   if(_length < 0) {
     _length = 0;

-  } else if(_length > (fLength - start)) {
-    _length = (fLength - start);
+  } else if(_length > (len - start)) {
+    _length = (len - start);

   }
 }
 
   }
 }
 

-inline UChar*
-UnicodeString::getArrayStart()
-{ return fArray; }
+inline char16_t*
+UnicodeString::getArrayStart() {
+  return (fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) ?
+    fUnion.fStackFields.fBuffer : fUnion.fFields.fArray;
+}
+
+inline const char16_t*
+UnicodeString::getArrayStart() const {
+  return (fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) ?
+    fUnion.fStackFields.fBuffer : fUnion.fFields.fArray;
+}
+
+//========================================
+// Default constructor
+//========================================
+
+inline
+UnicodeString::UnicodeString() {
+  fUnion.fStackFields.fLengthAndFlags=kShortString;
+}
+
+inline UnicodeString::UnicodeString(const std::nullptr_t /*text*/) {
+  fUnion.fStackFields.fLengthAndFlags=kShortString;
+}

 
 

-inline const UChar*
-UnicodeString::getArrayStart() const
-{ return fArray; }
+inline UnicodeString::UnicodeString(const std::nullptr_t /*text*/, int32_t /*length*/) {
+  fUnion.fStackFields.fLengthAndFlags=kShortString;
+}
+
+inline UnicodeString::UnicodeString(std::nullptr_t /*buffer*/, int32_t /*buffLength*/, int32_t /*buffCapacity*/) {
+  fUnion.fStackFields.fLengthAndFlags=kShortString;
+}

 
 //========================================
 // Read-only implementation methods
 //========================================
 
 //========================================
 // Read-only implementation methods
 //========================================

+inline UBool
+UnicodeString::hasShortLength() const {
+  return fUnion.fFields.fLengthAndFlags>=0;
+}
+

 inline int32_t
 inline int32_t

-UnicodeString::length() const
-{ return fLength; }
+UnicodeString::getShortLength() const {
+  // fLengthAndFlags must be non-negative -> short length >= 0
+  // and arithmetic or logical shift does not matter.
+  return fUnion.fFields.fLengthAndFlags>>kLengthShift;
+}
+
+inline int32_t
+UnicodeString::length() const {
+  return hasShortLength() ? getShortLength() : fUnion.fFields.fLength;
+}

 
 inline int32_t
 
 inline int32_t

-UnicodeString::getCapacity() const
-{ return fCapacity; }
+UnicodeString::getCapacity() const {
+  return (fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) ?
+    US_STACKBUF_SIZE : fUnion.fFields.fCapacity;
+}

 
 inline int32_t
 UnicodeString::hashCode() const
 
 inline int32_t
 UnicodeString::hashCode() const


@@ -3284,14 +3904,28 @@ UnicodeString::hashCode() const
 
 inline UBool
 UnicodeString::isBogus() const
 
 inline UBool
 UnicodeString::isBogus() const

-{ return (UBool)(fFlags & kIsBogus); }
+{ return (UBool)(fUnion.fFields.fLengthAndFlags & kIsBogus); }
+
+inline UBool
+UnicodeString::isWritable() const
+{ return (UBool)!(fUnion.fFields.fLengthAndFlags&(kOpenGetBuffer|kIsBogus)); }
+
+inline UBool
+UnicodeString::isBufferWritable() const
+{
+  return (UBool)(
+      !(fUnion.fFields.fLengthAndFlags&(kOpenGetBuffer|kIsBogus|kBufferIsReadonly)) &&
+      (!(fUnion.fFields.fLengthAndFlags&kRefCounted) || refCount()==1));
+}

 
 

-inline const UChar *
+inline const char16_t *

 UnicodeString::getBuffer() const {
 UnicodeString::getBuffer() const {

-  if(!(fFlags&(kIsBogus|kOpenGetBuffer))) {
-    return fArray;
+  if(fUnion.fFields.fLengthAndFlags&(kIsBogus|kOpenGetBuffer)) {
+    return nullptr;
+  } else if(fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) {
+    return fUnion.fStackFields.fBuffer;

   } else {
   } else {

-    return 0;
+    return fUnion.fFields.fArray;

   }
 }
 
   }
 }
 


@@ -3300,7 +3934,7 @@ UnicodeString::getBuffer() const {
 //========================================
 inline int8_t
 UnicodeString::doCompare(int32_t start,
 //========================================
 inline int8_t
 UnicodeString::doCompare(int32_t start,

-              int32_t length,
+              int32_t thisLength,

               const UnicodeString& srcText,
               int32_t srcStart,
               int32_t srcLength) const
               const UnicodeString& srcText,
               int32_t srcStart,
               int32_t srcLength) const


@@ -3309,7 +3943,7 @@ UnicodeString::doCompare(int32_t start,
     return (int8_t)!isBogus(); // 0 if both are bogus, 1 otherwise
   } else {
     srcText.pinIndices(srcStart, srcLength);
     return (int8_t)!isBogus(); // 0 if both are bogus, 1 otherwise
   } else {
     srcText.pinIndices(srcStart, srcLength);

-    return doCompare(start, length, srcText.fArray, srcStart, srcLength);
+    return doCompare(start, thisLength, srcText.getArrayStart(), srcStart, srcLength);

   }
 }
 
   }
 }
 


@@ -3319,10 +3953,8 @@ UnicodeString::operator== (const UnicodeString& text) const
   if(isBogus()) {
     return text.isBogus();
   } else {
   if(isBogus()) {
     return text.isBogus();
   } else {

-    return
-      !text.isBogus() &&
-      fLength == text.fLength &&
-      doCompare(0, fLength, text, 0, text.fLength) == 0;
+    int32_t len = length(), textLength = text.length();
+    return !text.isBogus() && len == textLength && doEquals(text, len);

   }
 }
 
   }
 }
 


@@ -3332,34 +3964,34 @@ UnicodeString::operator!= (const UnicodeString& text) const
 
 inline UBool
 UnicodeString::operator> (const UnicodeString& text) const
 
 inline UBool
 UnicodeString::operator> (const UnicodeString& text) const

-{ return doCompare(0, fLength, text, 0, text.fLength) == 1; }
+{ return doCompare(0, length(), text, 0, text.length()) == 1; }

 
 inline UBool
 UnicodeString::operator< (const UnicodeString& text) const
 
 inline UBool
 UnicodeString::operator< (const UnicodeString& text) const

-{ return doCompare(0, fLength, text, 0, text.fLength) == -1; }
+{ return doCompare(0, length(), text, 0, text.length()) == -1; }

 
 inline UBool
 UnicodeString::operator>= (const UnicodeString& text) const
 
 inline UBool
 UnicodeString::operator>= (const UnicodeString& text) const

-{ return doCompare(0, fLength, text, 0, text.fLength) != -1; }
+{ return doCompare(0, length(), text, 0, text.length()) != -1; }

 
 inline UBool
 UnicodeString::operator<= (const UnicodeString& text) const
 
 inline UBool
 UnicodeString::operator<= (const UnicodeString& text) const

-{ return doCompare(0, fLength, text, 0, text.fLength) != 1; }
+{ return doCompare(0, length(), text, 0, text.length()) != 1; }

 
 inline int8_t
 UnicodeString::compare(const UnicodeString& text) const
 
 inline int8_t
 UnicodeString::compare(const UnicodeString& text) const

-{ return doCompare(0, fLength, text, 0, text.fLength); }
+{ return doCompare(0, length(), text, 0, text.length()); }

 
 inline int8_t
 UnicodeString::compare(int32_t start,
                int32_t _length,
                const UnicodeString& srcText) const
 
 inline int8_t
 UnicodeString::compare(int32_t start,
                int32_t _length,
                const UnicodeString& srcText) const

-{ return doCompare(start, _length, srcText, 0, srcText.fLength); }
+{ return doCompare(start, _length, srcText, 0, srcText.length()); }

 
 inline int8_t
 
 inline int8_t

-UnicodeString::compare(const UChar *srcChars,
+UnicodeString::compare(ConstChar16Ptr srcChars,

                int32_t srcLength) const
                int32_t srcLength) const

-{ return doCompare(0, fLength, srcChars, 0, srcLength); }
+{ return doCompare(0, length(), srcChars, 0, srcLength); }

 
 inline int8_t
 UnicodeString::compare(int32_t start,
 
 inline int8_t
 UnicodeString::compare(int32_t start,


@@ -3372,13 +4004,13 @@ UnicodeString::compare(int32_t start,
 inline int8_t
 UnicodeString::compare(int32_t start,
                int32_t _length,
 inline int8_t
 UnicodeString::compare(int32_t start,
                int32_t _length,

-               const UChar *srcChars) const
+               const char16_t *srcChars) const

 { return doCompare(start, _length, srcChars, 0, _length); }
 
 inline int8_t
 UnicodeString::compare(int32_t start,
                int32_t _length,
 { return doCompare(start, _length, srcChars, 0, _length); }
 
 inline int8_t
 UnicodeString::compare(int32_t start,
                int32_t _length,

-               const UChar *srcChars,
+               const char16_t *srcChars,

                int32_t srcStart,
                int32_t srcLength) const
 { return doCompare(start, _length, srcChars, srcStart, srcLength); }
                int32_t srcStart,
                int32_t srcLength) const
 { return doCompare(start, _length, srcChars, srcStart, srcLength); }


@@ -3394,7 +4026,7 @@ UnicodeString::compareBetween(int32_t start,
 
 inline int8_t
 UnicodeString::doCompareCodePointOrder(int32_t start,
 
 inline int8_t
 UnicodeString::doCompareCodePointOrder(int32_t start,

-                                       int32_t length,
+                                       int32_t thisLength,

                                        const UnicodeString& srcText,
                                        int32_t srcStart,
                                        int32_t srcLength) const
                                        const UnicodeString& srcText,
                                        int32_t srcStart,
                                        int32_t srcLength) const


@@ -3403,24 +4035,24 @@ UnicodeString::doCompareCodePointOrder(int32_t start,
     return (int8_t)!isBogus(); // 0 if both are bogus, 1 otherwise
   } else {
     srcText.pinIndices(srcStart, srcLength);
     return (int8_t)!isBogus(); // 0 if both are bogus, 1 otherwise
   } else {
     srcText.pinIndices(srcStart, srcLength);

-    return doCompareCodePointOrder(start, length, srcText.fArray, srcStart, srcLength);
+    return doCompareCodePointOrder(start, thisLength, srcText.getArrayStart(), srcStart, srcLength);

   }
 }
 
 inline int8_t
 UnicodeString::compareCodePointOrder(const UnicodeString& text) const
   }
 }
 
 inline int8_t
 UnicodeString::compareCodePointOrder(const UnicodeString& text) const

-{ return doCompareCodePointOrder(0, fLength, text, 0, text.fLength); }
+{ return doCompareCodePointOrder(0, length(), text, 0, text.length()); }

 
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
                                      int32_t _length,
                                      const UnicodeString& srcText) const
 
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
                                      int32_t _length,
                                      const UnicodeString& srcText) const

-{ return doCompareCodePointOrder(start, _length, srcText, 0, srcText.fLength); }
+{ return doCompareCodePointOrder(start, _length, srcText, 0, srcText.length()); }

 
 inline int8_t
 
 inline int8_t

-UnicodeString::compareCodePointOrder(const UChar *srcChars,
+UnicodeString::compareCodePointOrder(ConstChar16Ptr srcChars,

                                      int32_t srcLength) const
                                      int32_t srcLength) const

-{ return doCompareCodePointOrder(0, fLength, srcChars, 0, srcLength); }
+{ return doCompareCodePointOrder(0, length(), srcChars, 0, srcLength); }

 
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
 
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,


@@ -3433,13 +4065,13 @@ UnicodeString::compareCodePointOrder(int32_t start,
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
                                      int32_t _length,
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
                                      int32_t _length,

-                                     const UChar *srcChars) const
+                                     const char16_t *srcChars) const

 { return doCompareCodePointOrder(start, _length, srcChars, 0, _length); }
 
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
                                      int32_t _length,
 { return doCompareCodePointOrder(start, _length, srcChars, 0, _length); }
 
 inline int8_t
 UnicodeString::compareCodePointOrder(int32_t start,
                                      int32_t _length,

-                                     const UChar *srcChars,
+                                     const char16_t *srcChars,

                                      int32_t srcStart,
                                      int32_t srcLength) const
 { return doCompareCodePointOrder(start, _length, srcChars, srcStart, srcLength); }
                                      int32_t srcStart,
                                      int32_t srcLength) const
 { return doCompareCodePointOrder(start, _length, srcChars, srcStart, srcLength); }


@@ -3455,7 +4087,7 @@ UnicodeString::compareCodePointOrderBetween(int32_t start,
 
 inline int8_t
 UnicodeString::doCaseCompare(int32_t start,
 
 inline int8_t
 UnicodeString::doCaseCompare(int32_t start,

-                             int32_t length,
+                             int32_t thisLength,

                              const UnicodeString &srcText,
                              int32_t srcStart,
                              int32_t srcLength,
                              const UnicodeString &srcText,
                              int32_t srcStart,
                              int32_t srcLength,


@@ -3465,13 +4097,13 @@ UnicodeString::doCaseCompare(int32_t start,
     return (int8_t)!isBogus(); // 0 if both are bogus, 1 otherwise
   } else {
     srcText.pinIndices(srcStart, srcLength);
     return (int8_t)!isBogus(); // 0 if both are bogus, 1 otherwise
   } else {
     srcText.pinIndices(srcStart, srcLength);

-    return doCaseCompare(start, length, srcText.fArray, srcStart, srcLength, options);
+    return doCaseCompare(start, thisLength, srcText.getArrayStart(), srcStart, srcLength, options);

   }
 }
 
 inline int8_t
 UnicodeString::caseCompare(const UnicodeString &text, uint32_t options) const {
   }
 }
 
 inline int8_t
 UnicodeString::caseCompare(const UnicodeString &text, uint32_t options) const {

-  return doCaseCompare(0, fLength, text, 0, text.fLength, options);
+  return doCaseCompare(0, length(), text, 0, text.length(), options);

 }
 
 inline int8_t
 }
 
 inline int8_t


@@ -3479,14 +4111,14 @@ UnicodeString::caseCompare(int32_t start,
                            int32_t _length,
                            const UnicodeString &srcText,
                            uint32_t options) const {
                            int32_t _length,
                            const UnicodeString &srcText,
                            uint32_t options) const {

-  return doCaseCompare(start, _length, srcText, 0, srcText.fLength, options);
+  return doCaseCompare(start, _length, srcText, 0, srcText.length(), options);

 }
 
 inline int8_t
 }
 
 inline int8_t

-UnicodeString::caseCompare(const UChar *srcChars,
+UnicodeString::caseCompare(ConstChar16Ptr srcChars,

                            int32_t srcLength,
                            uint32_t options) const {
                            int32_t srcLength,
                            uint32_t options) const {

-  return doCaseCompare(0, fLength, srcChars, 0, srcLength, options);
+  return doCaseCompare(0, length(), srcChars, 0, srcLength, options);

 }
 
 inline int8_t
 }
 
 inline int8_t


@@ -3502,7 +4134,7 @@ UnicodeString::caseCompare(int32_t start,
 inline int8_t
 UnicodeString::caseCompare(int32_t start,
                            int32_t _length,
 inline int8_t
 UnicodeString::caseCompare(int32_t start,
                            int32_t _length,

-                           const UChar *srcChars,
+                           const char16_t *srcChars,

                            uint32_t options) const {
   return doCaseCompare(start, _length, srcChars, 0, _length, options);
 }
                            uint32_t options) const {
   return doCaseCompare(start, _length, srcChars, 0, _length, options);
 }


@@ -3510,7 +4142,7 @@ UnicodeString::caseCompare(int32_t start,
 inline int8_t
 UnicodeString::caseCompare(int32_t start,
                            int32_t _length,
 inline int8_t
 UnicodeString::caseCompare(int32_t start,
                            int32_t _length,

-                           const UChar *srcChars,
+                           const char16_t *srcChars,

                            int32_t srcStart,
                            int32_t srcLength,
                            uint32_t options) const {
                            int32_t srcStart,
                            int32_t srcLength,
                            uint32_t options) const {


@@ -3545,38 +4177,38 @@ UnicodeString::indexOf(const UnicodeString& srcText,
 
 inline int32_t
 UnicodeString::indexOf(const UnicodeString& text) const
 
 inline int32_t
 UnicodeString::indexOf(const UnicodeString& text) const

-{ return indexOf(text, 0, text.fLength, 0, fLength); }
+{ return indexOf(text, 0, text.length(), 0, length()); }

 
 inline int32_t
 UnicodeString::indexOf(const UnicodeString& text,
                int32_t start) const {
   pinIndex(start);
 
 inline int32_t
 UnicodeString::indexOf(const UnicodeString& text,
                int32_t start) const {
   pinIndex(start);

-  return indexOf(text, 0, text.fLength, start, fLength - start);
+  return indexOf(text, 0, text.length(), start, length() - start);

 }
 
 inline int32_t
 UnicodeString::indexOf(const UnicodeString& text,
                int32_t start,
                int32_t _length) const
 }
 
 inline int32_t
 UnicodeString::indexOf(const UnicodeString& text,
                int32_t start,
                int32_t _length) const

-{ return indexOf(text, 0, text.fLength, start, _length); }
+{ return indexOf(text, 0, text.length(), start, _length); }

 
 inline int32_t
 
 inline int32_t

-UnicodeString::indexOf(const UChar *srcChars,
+UnicodeString::indexOf(const char16_t *srcChars,

                int32_t srcLength,
                int32_t start) const {
   pinIndex(start);
                int32_t srcLength,
                int32_t start) const {
   pinIndex(start);

-  return indexOf(srcChars, 0, srcLength, start, fLength - start);
+  return indexOf(srcChars, 0, srcLength, start, length() - start);

 }
 
 inline int32_t
 }
 
 inline int32_t

-UnicodeString::indexOf(const UChar *srcChars,
+UnicodeString::indexOf(ConstChar16Ptr srcChars,

                int32_t srcLength,
                int32_t start,
                int32_t _length) const
 { return indexOf(srcChars, 0, srcLength, start, _length); }
 
 inline int32_t
                int32_t srcLength,
                int32_t start,
                int32_t _length) const
 { return indexOf(srcChars, 0, srcLength, start, _length); }
 
 inline int32_t

-UnicodeString::indexOf(UChar c,
+UnicodeString::indexOf(char16_t c,

                int32_t start,
                int32_t _length) const
 { return doIndexOf(c, start, _length); }
                int32_t start,
                int32_t _length) const
 { return doIndexOf(c, start, _length); }


@@ -3588,40 +4220,40 @@ UnicodeString::indexOf(UChar32 c,
 { return doIndexOf(c, start, _length); }
 
 inline int32_t
 { return doIndexOf(c, start, _length); }
 
 inline int32_t

-UnicodeString::indexOf(UChar c) const
-{ return doIndexOf(c, 0, fLength); }
+UnicodeString::indexOf(char16_t c) const
+{ return doIndexOf(c, 0, length()); }

 
 inline int32_t
 UnicodeString::indexOf(UChar32 c) const
 
 inline int32_t
 UnicodeString::indexOf(UChar32 c) const

-{ return indexOf(c, 0, fLength); }
+{ return indexOf(c, 0, length()); }

 
 inline int32_t
 
 inline int32_t

-UnicodeString::indexOf(UChar c,
+UnicodeString::indexOf(char16_t c,

                int32_t start) const {
   pinIndex(start);
                int32_t start) const {
   pinIndex(start);

-  return doIndexOf(c, start, fLength - start);
+  return doIndexOf(c, start, length() - start);

 }
 
 inline int32_t
 UnicodeString::indexOf(UChar32 c,
                int32_t start) const {
   pinIndex(start);
 }
 
 inline int32_t
 UnicodeString::indexOf(UChar32 c,
                int32_t start) const {
   pinIndex(start);

-  return indexOf(c, start, fLength - start);
+  return indexOf(c, start, length() - start);

 }
 
 inline int32_t
 }
 
 inline int32_t

-UnicodeString::lastIndexOf(const UChar *srcChars,
+UnicodeString::lastIndexOf(ConstChar16Ptr srcChars,

                int32_t srcLength,
                int32_t start,
                int32_t _length) const
 { return lastIndexOf(srcChars, 0, srcLength, start, _length); }
 
 inline int32_t
                int32_t srcLength,
                int32_t start,
                int32_t _length) const
 { return lastIndexOf(srcChars, 0, srcLength, start, _length); }
 
 inline int32_t

-UnicodeString::lastIndexOf(const UChar *srcChars,
+UnicodeString::lastIndexOf(const char16_t *srcChars,

                int32_t srcLength,
                int32_t start) const {
   pinIndex(start);
                int32_t srcLength,
                int32_t start) const {
   pinIndex(start);

-  return lastIndexOf(srcChars, 0, srcLength, start, fLength - start);
+  return lastIndexOf(srcChars, 0, srcLength, start, length() - start);

 }
 
 inline int32_t
 }
 
 inline int32_t


@@ -3644,21 +4276,21 @@ inline int32_t
 UnicodeString::lastIndexOf(const UnicodeString& text,
                int32_t start,
                int32_t _length) const
 UnicodeString::lastIndexOf(const UnicodeString& text,
                int32_t start,
                int32_t _length) const

-{ return lastIndexOf(text, 0, text.fLength, start, _length); }
+{ return lastIndexOf(text, 0, text.length(), start, _length); }

 
 inline int32_t
 UnicodeString::lastIndexOf(const UnicodeString& text,
                int32_t start) const {
   pinIndex(start);
 
 inline int32_t
 UnicodeString::lastIndexOf(const UnicodeString& text,
                int32_t start) const {
   pinIndex(start);

-  return lastIndexOf(text, 0, text.fLength, start, fLength - start);
+  return lastIndexOf(text, 0, text.length(), start, length() - start);

 }
 
 inline int32_t
 UnicodeString::lastIndexOf(const UnicodeString& text) const
 }
 
 inline int32_t
 UnicodeString::lastIndexOf(const UnicodeString& text) const

-{ return lastIndexOf(text, 0, text.fLength, 0, fLength); }
+{ return lastIndexOf(text, 0, text.length(), 0, length()); }

 
 inline int32_t
 
 inline int32_t

-UnicodeString::lastIndexOf(UChar c,
+UnicodeString::lastIndexOf(char16_t c,

                int32_t start,
                int32_t _length) const
 { return doLastIndexOf(c, start, _length); }
                int32_t start,
                int32_t _length) const
 { return doLastIndexOf(c, start, _length); }


@@ -3671,31 +4303,31 @@ UnicodeString::lastIndexOf(UChar32 c,
 }
 
 inline int32_t
 }
 
 inline int32_t

-UnicodeString::lastIndexOf(UChar c) const
-{ return doLastIndexOf(c, 0, fLength); }
+UnicodeString::lastIndexOf(char16_t c) const
+{ return doLastIndexOf(c, 0, length()); }

 
 inline int32_t
 UnicodeString::lastIndexOf(UChar32 c) const {
 
 inline int32_t
 UnicodeString::lastIndexOf(UChar32 c) const {

-  return lastIndexOf(c, 0, fLength);
+  return lastIndexOf(c, 0, length());

 }
 
 inline int32_t
 }
 
 inline int32_t

-UnicodeString::lastIndexOf(UChar c,
+UnicodeString::lastIndexOf(char16_t c,

                int32_t start) const {
   pinIndex(start);
                int32_t start) const {
   pinIndex(start);

-  return doLastIndexOf(c, start, fLength - start);
+  return doLastIndexOf(c, start, length() - start);

 }
 
 inline int32_t
 UnicodeString::lastIndexOf(UChar32 c,
                int32_t start) const {
   pinIndex(start);
 }
 
 inline int32_t
 UnicodeString::lastIndexOf(UChar32 c,
                int32_t start) const {
   pinIndex(start);

-  return lastIndexOf(c, start, fLength - start);
+  return lastIndexOf(c, start, length() - start);

 }
 
 inline UBool
 UnicodeString::startsWith(const UnicodeString& text) const
 }
 
 inline UBool
 UnicodeString::startsWith(const UnicodeString& text) const

-{ return compare(0, text.fLength, text, 0, text.fLength) == 0; }
+{ return compare(0, text.length(), text, 0, text.length()) == 0; }

 
 inline UBool
 UnicodeString::startsWith(const UnicodeString& srcText,
 
 inline UBool
 UnicodeString::startsWith(const UnicodeString& srcText,


@@ -3704,48 +4336,53 @@ UnicodeString::startsWith(const UnicodeString& srcText,
 { return doCompare(0, srcLength, srcText, srcStart, srcLength) == 0; }
 
 inline UBool
 { return doCompare(0, srcLength, srcText, srcStart, srcLength) == 0; }
 
 inline UBool

-UnicodeString::startsWith(const UChar *srcChars,
-              int32_t srcLength) const
-{ return doCompare(0, srcLength, srcChars, 0, srcLength) == 0; }
+UnicodeString::startsWith(ConstChar16Ptr srcChars, int32_t srcLength) const {
+  if(srcLength < 0) {
+    srcLength = u_strlen(toUCharPtr(srcChars));
+  }
+  return doCompare(0, srcLength, srcChars, 0, srcLength) == 0;
+}

 
 inline UBool
 
 inline UBool

-UnicodeString::startsWith(const UChar *srcChars,
-              int32_t srcStart,
-              int32_t srcLength) const
-{ return doCompare(0, srcLength, srcChars, srcStart, srcLength) == 0;}
+UnicodeString::startsWith(const char16_t *srcChars, int32_t srcStart, int32_t srcLength) const {
+  if(srcLength < 0) {
+    srcLength = u_strlen(toUCharPtr(srcChars));
+  }
+  return doCompare(0, srcLength, srcChars, srcStart, srcLength) == 0;
+}

 
 inline UBool
 UnicodeString::endsWith(const UnicodeString& text) const
 
 inline UBool
 UnicodeString::endsWith(const UnicodeString& text) const

-{ return doCompare(fLength - text.fLength, text.fLength,
-           text, 0, text.fLength) == 0; }
+{ return doCompare(length() - text.length(), text.length(),
+           text, 0, text.length()) == 0; }

 
 inline UBool
 UnicodeString::endsWith(const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength) const {
   srcText.pinIndices(srcStart, srcLength);
 
 inline UBool
 UnicodeString::endsWith(const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength) const {
   srcText.pinIndices(srcStart, srcLength);

-  return doCompare(fLength - srcLength, srcLength,
+  return doCompare(length() - srcLength, srcLength,

                    srcText, srcStart, srcLength) == 0;
 }
 
 inline UBool
                    srcText, srcStart, srcLength) == 0;
 }
 
 inline UBool

-UnicodeString::endsWith(const UChar *srcChars,
+UnicodeString::endsWith(ConstChar16Ptr srcChars,

             int32_t srcLength) const {
   if(srcLength < 0) {
             int32_t srcLength) const {
   if(srcLength < 0) {

-    srcLength = u_strlen(srcChars);
+    srcLength = u_strlen(toUCharPtr(srcChars));

   }
   }

-  return doCompare(fLength - srcLength, srcLength,
+  return doCompare(length() - srcLength, srcLength,

                    srcChars, 0, srcLength) == 0;
 }
 
 inline UBool
                    srcChars, 0, srcLength) == 0;
 }
 
 inline UBool

-UnicodeString::endsWith(const UChar *srcChars,
+UnicodeString::endsWith(const char16_t *srcChars,

             int32_t srcStart,
             int32_t srcLength) const {
   if(srcLength < 0) {
             int32_t srcStart,
             int32_t srcLength) const {
   if(srcLength < 0) {

-    srcLength = u_strlen(srcChars + srcStart);
+    srcLength = u_strlen(toUCharPtr(srcChars + srcStart));

   }
   }

-  return doCompare(fLength - srcLength, srcLength,
+  return doCompare(length() - srcLength, srcLength,

                    srcChars, srcStart, srcLength) == 0;
 }
 
                    srcChars, srcStart, srcLength) == 0;
 }
 


@@ -3756,7 +4393,7 @@ inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,
                const UnicodeString& srcText)
 UnicodeString::replace(int32_t start,
                int32_t _length,
                const UnicodeString& srcText)

-{ return doReplace(start, _length, srcText, 0, srcText.fLength); }
+{ return doReplace(start, _length, srcText, 0, srcText.length()); }

 
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
 
 inline UnicodeString&
 UnicodeString::replace(int32_t start,


@@ -3769,14 +4406,14 @@ UnicodeString::replace(int32_t start,
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,

-               const UChar *srcChars,
+               ConstChar16Ptr srcChars,

                int32_t srcLength)
 { return doReplace(start, _length, srcChars, 0, srcLength); }
 
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,
                int32_t srcLength)
 { return doReplace(start, _length, srcChars, 0, srcLength); }
 
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,

-               const UChar *srcChars,
+               const char16_t *srcChars,

                int32_t srcStart,
                int32_t srcLength)
 { return doReplace(start, _length, srcChars, srcStart, srcLength); }
                int32_t srcStart,
                int32_t srcLength)
 { return doReplace(start, _length, srcChars, srcStart, srcLength); }


@@ -3784,25 +4421,14 @@ UnicodeString::replace(int32_t start,
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,
 inline UnicodeString&
 UnicodeString::replace(int32_t start,
                int32_t _length,

-               UChar srcChar)
+               char16_t srcChar)

 { return doReplace(start, _length, &srcChar, 0, 1); }
 
 { return doReplace(start, _length, &srcChar, 0, 1); }
 

-inline UnicodeString&
-UnicodeString::replace(int32_t start,
-               int32_t _length,
-               UChar32 srcChar) {
-  UChar buffer[U16_MAX_LENGTH];
-  int32_t count = 0;
-  UBool isError = FALSE;
-  U16_APPEND(buffer, count, U16_MAX_LENGTH, srcChar, isError);
-  return doReplace(start, _length, buffer, 0, count);
-}
-

 inline UnicodeString&
 UnicodeString::replaceBetween(int32_t start,
                   int32_t limit,
                   const UnicodeString& srcText)
 inline UnicodeString&
 UnicodeString::replaceBetween(int32_t start,
                   int32_t limit,
                   const UnicodeString& srcText)

-{ return doReplace(start, limit - start, srcText, 0, srcText.fLength); }
+{ return doReplace(start, limit - start, srcText, 0, srcText.length()); }

 
 inline UnicodeString&
 UnicodeString::replaceBetween(int32_t start,
 
 inline UnicodeString&
 UnicodeString::replaceBetween(int32_t start,


@@ -3815,16 +4441,16 @@ UnicodeString::replaceBetween(int32_t start,
 inline UnicodeString&
 UnicodeString::findAndReplace(const UnicodeString& oldText,
                   const UnicodeString& newText)
 inline UnicodeString&
 UnicodeString::findAndReplace(const UnicodeString& oldText,
                   const UnicodeString& newText)

-{ return findAndReplace(0, fLength, oldText, 0, oldText.fLength,
-            newText, 0, newText.fLength); }
+{ return findAndReplace(0, length(), oldText, 0, oldText.length(),
+            newText, 0, newText.length()); }

 
 inline UnicodeString&
 UnicodeString::findAndReplace(int32_t start,
                   int32_t _length,
                   const UnicodeString& oldText,
                   const UnicodeString& newText)
 
 inline UnicodeString&
 UnicodeString::findAndReplace(int32_t start,
                   int32_t _length,
                   const UnicodeString& oldText,
                   const UnicodeString& newText)

-{ return findAndReplace(start, _length, oldText, 0, oldText.fLength,
-            newText, 0, newText.fLength); }
+{ return findAndReplace(start, _length, oldText, 0, oldText.length(),
+            newText, 0, newText.length()); }

 
 // ============================
 // extract
 
 // ============================
 // extract


@@ -3833,12 +4459,12 @@ inline void
 UnicodeString::doExtract(int32_t start,
              int32_t _length,
              UnicodeString& target) const
 UnicodeString::doExtract(int32_t start,
              int32_t _length,
              UnicodeString& target) const

-{ target.replace(0, target.fLength, *this, start, _length); }
+{ target.replace(0, target.length(), *this, start, _length); }

 
 inline void
 UnicodeString::extract(int32_t start,
                int32_t _length,
 
 inline void
 UnicodeString::extract(int32_t start,
                int32_t _length,

-               UChar *target,
+               Char16Ptr target,

                int32_t targetStart) const
 { doExtract(start, _length, target, targetStart); }
 
                int32_t targetStart) const
 { doExtract(start, _length, target, targetStart); }
 


@@ -3866,92 +4492,86 @@ UnicodeString::extract(int32_t start,
 inline void
 UnicodeString::extractBetween(int32_t start,
                   int32_t limit,
 inline void
 UnicodeString::extractBetween(int32_t start,
                   int32_t limit,

-                  UChar *dst,
+                  char16_t *dst,

                   int32_t dstStart) const {
   pinIndex(start);
   pinIndex(limit);
   doExtract(start, limit - start, dst, dstStart);
 }
 
                   int32_t dstStart) const {
   pinIndex(start);
   pinIndex(limit);
   doExtract(start, limit - start, dst, dstStart);
 }
 

-inline UChar
+inline UnicodeString
+UnicodeString::tempSubStringBetween(int32_t start, int32_t limit) const {
+    return tempSubString(start, limit - start);
+}
+
+inline char16_t

 UnicodeString::doCharAt(int32_t offset) const
 {
 UnicodeString::doCharAt(int32_t offset) const
 {

-  if((uint32_t)offset < (uint32_t)fLength) {
-    return fArray[offset];
+  if((uint32_t)offset < (uint32_t)length()) {
+    return getArrayStart()[offset];

   } else {
     return kInvalidUChar;
   }
 }
 
   } else {
     return kInvalidUChar;
   }
 }
 

-inline UChar
+inline char16_t

 UnicodeString::charAt(int32_t offset) const
 { return doCharAt(offset); }
 
 UnicodeString::charAt(int32_t offset) const
 { return doCharAt(offset); }
 

-inline UChar
+inline char16_t

 UnicodeString::operator[] (int32_t offset) const
 { return doCharAt(offset); }
 
 UnicodeString::operator[] (int32_t offset) const
 { return doCharAt(offset); }
 

-inline UChar32
-UnicodeString::char32At(int32_t offset) const
-{
-  if((uint32_t)offset < (uint32_t)fLength) {
-    UChar32 c;
-    U16_GET(fArray, 0, offset, fLength, c);
-    return c;
-  } else {
-    return kInvalidUChar;
-  }
+inline UBool
+UnicodeString::isEmpty() const {
+  // Arithmetic or logical right shift does not matter: only testing for 0.
+  return (fUnion.fFields.fLengthAndFlags>>kLengthShift) == 0;

 }
 
 }
 

-inline int32_t
-UnicodeString::getChar32Start(int32_t offset) const {
-  if((uint32_t)offset < (uint32_t)fLength) {
-    U16_SET_CP_START(fArray, 0, offset);
-    return offset;
-  } else {
-    return 0;
-  }
+//========================================
+// Write implementation methods
+//========================================
+inline void
+UnicodeString::setZeroLength() {
+  fUnion.fFields.fLengthAndFlags &= kAllStorageFlags;

 }
 
 }
 

-inline int32_t
-UnicodeString::getChar32Limit(int32_t offset) const {
-  if((uint32_t)offset < (uint32_t)fLength) {
-    U16_SET_CP_LIMIT(fArray, 0, offset, fLength);
-    return offset;
+inline void
+UnicodeString::setShortLength(int32_t len) {
+  // requires 0 <= len <= kMaxShortLength
+  fUnion.fFields.fLengthAndFlags =
+    (int16_t)((fUnion.fFields.fLengthAndFlags & kAllStorageFlags) | (len << kLengthShift));
+}
+
+inline void
+UnicodeString::setLength(int32_t len) {
+  if(len <= kMaxShortLength) {
+    setShortLength(len);

   } else {
   } else {

-    return fLength;
+    fUnion.fFields.fLengthAndFlags |= kLengthIsLarge;
+    fUnion.fFields.fLength = len;

   }
 }
 
   }
 }
 

-inline UBool
-UnicodeString::isEmpty() const {
-  return fLength == 0;
+inline void
+UnicodeString::setToEmpty() {
+  fUnion.fFields.fLengthAndFlags = kShortString;

 }
 
 }
 

-//========================================
-// Write implementation methods
-//========================================
-inline const UChar *
-UnicodeString::getTerminatedBuffer() {
-  if(fFlags&(kIsBogus|kOpenGetBuffer)) {
-    return 0;
-  } else if(fLength<fCapacity && fArray[fLength]==0) {
-    return fArray;
-  } else if(cloneArrayIfNeeded(fLength+1)) {
-    fArray[fLength]=0;
-    return fArray;
-  } else {
-    return 0;
-  }
+inline void
+UnicodeString::setArray(char16_t *array, int32_t len, int32_t capacity) {
+  setLength(len);
+  fUnion.fFields.fArray = array;
+  fUnion.fFields.fCapacity = capacity;

 }
 
 inline UnicodeString&
 }
 
 inline UnicodeString&

-UnicodeString::operator= (UChar ch)
-{ return doReplace(0, fLength, &ch, 0, 1); }
+UnicodeString::operator= (char16_t ch)
+{ return doReplace(0, length(), &ch, 0, 1); }

 
 inline UnicodeString&
 UnicodeString::operator= (UChar32 ch)
 
 inline UnicodeString&
 UnicodeString::operator= (UChar32 ch)

-{ return replace(0, fLength, ch); }
+{ return replace(0, length(), ch); }

 
 inline UnicodeString&
 UnicodeString::setTo(const UnicodeString& srcText,
 
 inline UnicodeString&
 UnicodeString::setTo(const UnicodeString& srcText,


@@ -3959,7 +4579,7 @@ UnicodeString::setTo(const UnicodeString& srcText,
              int32_t srcLength)
 {
   unBogus();
              int32_t srcLength)
 {
   unBogus();

-  return doReplace(0, fLength, srcText, srcStart, srcLength);
+  return doReplace(0, length(), srcText, srcStart, srcLength);

 }
 
 inline UnicodeString&
 }
 
 inline UnicodeString&


@@ -3968,89 +4588,75 @@ UnicodeString::setTo(const UnicodeString& srcText,
 {
   unBogus();
   srcText.pinIndex(srcStart);
 {
   unBogus();
   srcText.pinIndex(srcStart);

-  return doReplace(0, fLength, srcText, srcStart, srcText.fLength - srcStart);
+  return doReplace(0, length(), srcText, srcStart, srcText.length() - srcStart);

 }
 
 inline UnicodeString&
 UnicodeString::setTo(const UnicodeString& srcText)
 {
 }
 
 inline UnicodeString&
 UnicodeString::setTo(const UnicodeString& srcText)
 {

-  unBogus();
-  return doReplace(0, fLength, srcText, 0, srcText.fLength);
+  return copyFrom(srcText);

 }
 
 inline UnicodeString&
 }
 
 inline UnicodeString&

-UnicodeString::setTo(const UChar *srcChars,
+UnicodeString::setTo(const char16_t *srcChars,

              int32_t srcLength)
 {
   unBogus();
              int32_t srcLength)
 {
   unBogus();

-  return doReplace(0, fLength, srcChars, 0, srcLength);
+  return doReplace(0, length(), srcChars, 0, srcLength);

 }
 
 inline UnicodeString&
 }
 
 inline UnicodeString&

-UnicodeString::setTo(UChar srcChar)
+UnicodeString::setTo(char16_t srcChar)

 {
   unBogus();
 {
   unBogus();

-  return doReplace(0, fLength, &srcChar, 0, 1);
+  return doReplace(0, length(), &srcChar, 0, 1);

 }
 
 inline UnicodeString&
 UnicodeString::setTo(UChar32 srcChar)
 {
   unBogus();
 }
 
 inline UnicodeString&
 UnicodeString::setTo(UChar32 srcChar)
 {
   unBogus();

-  return replace(0, fLength, srcChar);
+  return replace(0, length(), srcChar);

 }
 
 }
 

-inline UnicodeString&
-UnicodeString::operator+= (UChar ch)
-{ return doReplace(fLength, 0, &ch, 0, 1); }
-
-inline UnicodeString&
-UnicodeString::operator+= (UChar32 ch) {
-  UChar buffer[U16_MAX_LENGTH];
-  int32_t _length = 0;
-  UBool isError = FALSE;
-  U16_APPEND(buffer, _length, U16_MAX_LENGTH, ch, isError);
-  return doReplace(fLength, 0, buffer, 0, _length);
-}
-
-inline UnicodeString&
-UnicodeString::operator+= (const UnicodeString& srcText)
-{ return doReplace(fLength, 0, srcText, 0, srcText.fLength); }
-

 inline UnicodeString&
 UnicodeString::append(const UnicodeString& srcText,
               int32_t srcStart,
               int32_t srcLength)
 inline UnicodeString&
 UnicodeString::append(const UnicodeString& srcText,
               int32_t srcStart,
               int32_t srcLength)

-{ return doReplace(fLength, 0, srcText, srcStart, srcLength); }
+{ return doAppend(srcText, srcStart, srcLength); }

 
 inline UnicodeString&
 UnicodeString::append(const UnicodeString& srcText)
 
 inline UnicodeString&
 UnicodeString::append(const UnicodeString& srcText)

-{ return doReplace(fLength, 0, srcText, 0, srcText.fLength); }
+{ return doAppend(srcText, 0, srcText.length()); }

 
 inline UnicodeString&
 
 inline UnicodeString&

-UnicodeString::append(const UChar *srcChars,
+UnicodeString::append(const char16_t *srcChars,

               int32_t srcStart,
               int32_t srcLength)
               int32_t srcStart,
               int32_t srcLength)

-{ return doReplace(fLength, 0, srcChars, srcStart, srcLength); }
+{ return doAppend(srcChars, srcStart, srcLength); }

 
 inline UnicodeString&
 
 inline UnicodeString&

-UnicodeString::append(const UChar *srcChars,
+UnicodeString::append(ConstChar16Ptr srcChars,

               int32_t srcLength)
               int32_t srcLength)

-{ return doReplace(fLength, 0, srcChars, 0, srcLength); }
+{ return doAppend(srcChars, 0, srcLength); }
+
+inline UnicodeString&
+UnicodeString::append(char16_t srcChar)
+{ return doAppend(&srcChar, 0, 1); }

 
 inline UnicodeString&
 
 inline UnicodeString&

-UnicodeString::append(UChar srcChar)
-{ return doReplace(fLength, 0, &srcChar, 0, 1); }
+UnicodeString::operator+= (char16_t ch)
+{ return doAppend(&ch, 0, 1); }

 
 inline UnicodeString&
 
 inline UnicodeString&

-UnicodeString::append(UChar32 srcChar) {
-  UChar buffer[U16_MAX_LENGTH];
-  int32_t _length = 0;
-  UBool isError = FALSE;
-  U16_APPEND(buffer, _length, U16_MAX_LENGTH, srcChar, isError);
-  return doReplace(fLength, 0, buffer, 0, _length);
+UnicodeString::operator+= (UChar32 ch) {
+  return append(ch);

 }
 
 }
 

+inline UnicodeString&
+UnicodeString::operator+= (const UnicodeString& srcText)
+{ return doAppend(srcText, 0, srcText.length()); }
+

 inline UnicodeString&
 UnicodeString::insert(int32_t start,
               const UnicodeString& srcText,
 inline UnicodeString&
 UnicodeString::insert(int32_t start,
               const UnicodeString& srcText,


@@ -4061,24 +4667,24 @@ UnicodeString::insert(int32_t start,
 inline UnicodeString&
 UnicodeString::insert(int32_t start,
               const UnicodeString& srcText)
 inline UnicodeString&
 UnicodeString::insert(int32_t start,
               const UnicodeString& srcText)

-{ return doReplace(start, 0, srcText, 0, srcText.fLength); }
+{ return doReplace(start, 0, srcText, 0, srcText.length()); }

 
 inline UnicodeString&
 UnicodeString::insert(int32_t start,
 
 inline UnicodeString&
 UnicodeString::insert(int32_t start,

-              const UChar *srcChars,
+              const char16_t *srcChars,

               int32_t srcStart,
               int32_t srcLength)
 { return doReplace(start, 0, srcChars, srcStart, srcLength); }
 
 inline UnicodeString&
 UnicodeString::insert(int32_t start,
               int32_t srcStart,
               int32_t srcLength)
 { return doReplace(start, 0, srcChars, srcStart, srcLength); }
 
 inline UnicodeString&
 UnicodeString::insert(int32_t start,

-              const UChar *srcChars,
+              ConstChar16Ptr srcChars,

               int32_t srcLength)
 { return doReplace(start, 0, srcChars, 0, srcLength); }
 
 inline UnicodeString&
 UnicodeString::insert(int32_t start,
               int32_t srcLength)
 { return doReplace(start, 0, srcChars, 0, srcLength); }
 
 inline UnicodeString&
 UnicodeString::insert(int32_t start,

-              UChar srcChar)
+              char16_t srcChar)

 { return doReplace(start, 0, &srcChar, 0, 1); }
 
 inline UnicodeString&
 { return doReplace(start, 0, &srcChar, 0, 1); }
 
 inline UnicodeString&


@@ -4092,9 +4698,9 @@ UnicodeString::remove()
 {
   // remove() of a bogus string makes the string empty and non-bogus
   if(isBogus()) {
 {
   // remove() of a bogus string makes the string empty and non-bogus
   if(isBogus()) {

-    unBogus();
+    setToEmpty();

   } else {
   } else {

-    fLength = 0;
+    setZeroLength();

   }
   return *this;
 }
   }
   return *this;
 }


@@ -4103,12 +4709,11 @@ inline UnicodeString&
 UnicodeString::remove(int32_t start,
              int32_t _length)
 {
 UnicodeString::remove(int32_t start,
              int32_t _length)
 {

-  if(start <= 0 && _length == INT32_MAX) {
-    // remove(guaranteed everything) of a bogus string makes the string empty and non-bogus
-    return remove();
-  } else {
+    if(start <= 0 && _length == INT32_MAX) {
+        // remove(guaranteed everything) of a bogus string makes the string empty and non-bogus
+        return remove();
+    }

     return doReplace(start, _length, NULL, 0, 0);
     return doReplace(start, _length, NULL, 0, 0);

-  }

 }
 
 inline UnicodeString&
 }
 
 inline UnicodeString&


@@ -4116,6 +4721,12 @@ UnicodeString::removeBetween(int32_t start,
                 int32_t limit)
 { return doReplace(start, limit - start, NULL, 0, 0); }
 
                 int32_t limit)
 { return doReplace(start, limit - start, NULL, 0, 0); }
 

+inline UnicodeString &
+UnicodeString::retainBetween(int32_t start, int32_t limit) {
+  truncate(limit);
+  return doReplace(0, start, NULL, 0, 0);
+}
+

 inline UBool
 UnicodeString::truncate(int32_t targetLength)
 {
 inline UBool
 UnicodeString::truncate(int32_t targetLength)
 {


@@ -4123,8 +4734,8 @@ UnicodeString::truncate(int32_t targetLength)
     // truncate(0) of a bogus string makes the string empty and non-bogus
     unBogus();
     return FALSE;
     // truncate(0) of a bogus string makes the string empty and non-bogus
     unBogus();
     return FALSE;

-  } else if((uint32_t)targetLength < (uint32_t)fLength) {
-    fLength = targetLength;
+  } else if((uint32_t)targetLength < (uint32_t)length()) {
+    setLength(targetLength);

     return TRUE;
   } else {
     return FALSE;
     return TRUE;
   } else {
     return FALSE;


@@ -4133,7 +4744,7 @@ UnicodeString::truncate(int32_t targetLength)
 
 inline UnicodeString&
 UnicodeString::reverse()
 
 inline UnicodeString&
 UnicodeString::reverse()

-{ return doReverse(0, fLength); }
+{ return doReverse(0, length()); }

 
 inline UnicodeString&
 UnicodeString::reverse(int32_t start,
 
 inline UnicodeString&
 UnicodeString::reverse(int32_t start,


@@ -4141,5 +4752,6 @@ UnicodeString::reverse(int32_t start,
 { return doReverse(start, _length); }
 
 U_NAMESPACE_END
 { return doReverse(start, _length); }
 
 U_NAMESPACE_END

+#endif // U_SHOW_CPLUSPLUS_API

 
 #endif
 
 #endif