-This class provides support for regular expressions matching and also
-replacement. It is built on top of either the system library (if it has support
-for POSIX regular expressions - which is the case of the most modern Unices) or
-uses a version of Henry Spencer's library from tcl.
+It is built on top of either the system library (if it has support
+for POSIX regular expressions - which is the case of the most modern
+Unices) or uses the built in Henry Spencer's library. Henry Spencer
+would appreciate being given credit in the documentation of software
+which uses his library, but that is not a requirement.
+
+Regular expressions, as defined by POSIX, come in two flavours: {\it extended}
+and {\it basic}. The builtin library also adds a third flavour
+of expression \helpref{advanced}{wxresyn}, which is not available
+when using the system library.
+
+Unicode is fully supported only when using the builtin library.
+When using the system library in Unicode mode, the expressions and data
+are translated to the default 8-bit encoding before being passed to
+the library.
+
+On platforms where a system library is available, the default is to use
+the builtin library for Unicode builds, and the system library otherwise.
+It is possible to use the other if preferred by selecting it when building
+the wxWidgets.