+ <para>The <filename>/etc/apt/sources.list.d</filename> directory provides
+ a way to add sources.list entries in separate files.
+ Two different file formats are allowed as described in the next two sections.
+ Filenames need to have either the extension <filename>.list</filename> or
+ <filename>.sources</filename> depending on the contained format.
+ The filenames may only contain letters (a-z and A-Z),
+ digits (0-9), underscore (_), hyphen (-) and period (.) characters.
+ Otherwise APT will print a notice that it has ignored a file, unless that
+ file matches a pattern in the <literal>Dir::Ignore-Files-Silently</literal>
+ configuration list - in which case it will be silently ignored.</para>
+ </refsect1>
+
+ <refsect1><title>one line style format</title>
+ <para>
+ Files in this format have the extension <filename>.list</filename>.
+ Each line specifying a source starts with a type (e.g. <literal>deb-src</literal>)
+ followed by options and arguments for this type.
+
+ Individual entries cannot be continued onto a following line. Empty lines
+ are ignored, and a <literal>#</literal> character anywhere on a line marks
+ the remainder of that line as a comment. Consequently an entry can be
+ disabled by commenting out the entire line.
+
+ If options should be provided they are separated by spaces and all of
+ them together are enclosed by square brackets (<literal>[]</literal>)
+ included in the line after the type separated from it with a space.
+ If an option allows multiple values these are separated from each other
+ with a comma (<literal>,</literal>). An option name is separated from its
+ value(s) by a equal sign (<literal>=</literal>). Multivalue options have
+ also <literal>-=</literal> and <literal>+=</literal> as separator which
+ instead of replacing the default with the given value(s) modify the default
+ value(s) to remove or include the given values.
+ </para><para>
+ This is the traditional format and supported by all apt versions.
+ Note that not all options as described below are supported by all apt versions.
+ Note also that some older applications parsing this format on its own might not
+ expect to encounter options as they were uncommon before the introduction of
+ multi-architecture support.
+ </para>
+ </refsect1>
+
+ <refsect1><title>deb822 style format</title>
+ <para>
+ Files in this format have the extension <filename>.sources</filename>.
+ The format is similar in syntax to other files used by Debian and its
+ derivatives, like the metadata itself apt will download from the configured
+ sources or the <filename>debian/control</filename> file in a Debian source package.
+
+ Individual entries are separated by an empty line, additional empty
+ lines are ignored, and a <literal>#</literal> character at the start of
+ the line marks the entire line as a comment. An entry can hence be
+ disabled by commenting out each line belonging to the stanza, but it is
+ usually easier to add the field "Enabled: no" to the stanza to disable
+ the entry. Removing the field or setting it to yes reenables it.
+
+ Options have the same syntax as every other field: A fieldname separated by
+ a colon (<literal>:</literal>) and optionally spaces from its value(s).
+ Note especially that multiple values are separated by spaces, not by
+ commas as in the one line format. Multivalue fields like <literal>Architectures</literal>
+ also have <literal>Architectures-Add</literal> and <literal>Architectures-Remove</literal>
+ to modify the default value rather than replacing it.
+ </para><para>
+ This is a new format supported by apt itself since version 1.1. Previous
+ versions ignore such files with a notice message as described earlier.
+ It is intended to make this format gradually the default format and
+ deprecating the previously described one line style format as it is
+ easier to create, extend and modify by humans and machines alike
+ especially if a lot of sources and/or options are involved.
+
+ Developers who are working with and/or parsing apt sources are highly
+ encouraged to add support for this format and to contact the APT team
+ to coordinate and share this work. Users can freely adopt this format
+ already, but could encounter problems with software not supporting
+ the format yet.
+ </para>