doc/{user,protocol}: add a list of supported tags

Makefile.am

@@ -2109,7 +2109,9 @@ developer_DATA = $(wildcard doc/developer/*.html)
 
 DOCBOOK_HTML = $(patsubst %.xml,%/index.html,$(DOCBOOK_FILES))
 
-$(DOCBOOK_HTML): %/index.html: %.xml
+DOCBOOK_INCLUDES = $(wildcard $(srcdir)/doc/include/*.xml)
+
+$(DOCBOOK_HTML): %/index.html: %.xml $(DOCBOOK_INCLUDES)
 	$(XMLTO) -o $(@D) --stringparam chunker.output.encoding=utf-8 html --stringparam use.id.as.filename=1 $<
 
 doc/api/html/index.html: doc/doxygen.conf

doc/include/tags.xml

+<?xml version='1.0' encoding="utf-8"?>
+<!DOCTYPE itemizedlist PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+                              "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
+
+<itemizedlist>
+  <listitem>
+    <para>
+      <varname>artist</varname>: the artist name.  Its meaning is not
+      well-defined; see <varname>composer</varname> and
+      <varname>performer</varname> for more specific tags.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>artistsort</varname>: same as
+      <varname>artist</varname>, but for sorting.  This usually omits
+      prefixes such as "The".
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>album</varname>: the album name.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>albumsort</varname>: same as <varname>album</varname>,
+      but for sorting.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>albumartist</varname>: on multi-artist albums, this is
+      the artist name which shall be used for the whole album.  The
+      exact meaning of this tag is not well-defined.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>albumartistsort</varname>: same as
+      <varname>albumartist</varname>, but for sorting.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>title</varname>: the song title.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>track</varname>: the track number within the album.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>name</varname>: a name for this song.  This is not the
+      song title.  The exact meaning of this tag is not well-defined.
+      It is often used by badly configured internet radio stations
+      with broken tags to squeeze both the artist name and the song
+      title in one tag.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>genre</varname>: the music genre.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>date</varname>: the song's release date.  This is
+      usually a 4-digit year.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>composer</varname>: the artist who composed the song.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>performer</varname>: the artist who performed the song.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>comment</varname>: a human-readable comment about this
+      song.  The exact meaning of this tag is not well-defined.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>disc</varname>: the disc number in a multi-disc album.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>musicbrainz_artistid</varname>: the artist id in the
+      <ulink
+      url="http://musicbrainz.org/doc/MusicBrainzTag">MusicBrainz</ulink>
+      database.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>musicbrainz_albumid</varname>: the album id in the
+      <ulink
+      url="http://musicbrainz.org/doc/MusicBrainzTag">MusicBrainz</ulink>
+      database.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>musicbrainz_albumartistid</varname>: the album artist
+      id in the <ulink
+      url="http://musicbrainz.org/doc/MusicBrainzTag">MusicBrainz</ulink>
+      database.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>musicbrainz_trackid</varname>: the track id in the
+      <ulink
+      url="http://musicbrainz.org/doc/MusicBrainzTag">MusicBrainz</ulink>
+      database.
+    </para>
+  </listitem>
+
+  <listitem>
+    <para>
+      <varname>musicbrainz_releasetrackid</varname>: the release track
+      id in the <ulink
+      url="http://musicbrainz.org/doc/MusicBrainzTag">MusicBrainz</ulink>
+      database.
+    </para>
+  </listitem>
+</itemizedlist>

doc/mpd.conf.5

@@ -176,10 +176,8 @@ when saving playlists.  The default is "no".
 .TP
 .B metadata_to_use <tags>
 This specifies the tag types that will be scanned for and made available to
-clients.  Possible values are artist, album, title,
-track, name, genre, date, composer, performer, comment, disc,
-musicbrainz_artistid, musicbrainz_albumid, musicbrainz_albumartistid,
-musicbrainz_releasetrackid, musicbrainz_trackid.  Multiple tags may be specified
+clients.  Possible values are listed in the MPD user manual.
+Multiple tags may be specified
 as a comma separated list.
 An example value is "artist,album,title,track".  The special value "none" may
 be used alone to disable all metadata.  The default is to use all known tag

doc/mpdconf.example

@@ -115,7 +115,7 @@
 #
 # This setting defines a list of tag types that will be extracted during the
 # audio file discovery process. The complete list of possible values can be
-# found in the mpd.conf man page.
+# found in the user manual.
 #metadata_to_use	"artist,album,title,track,name,genre,date,composer,performer,disc"
 #
 # This setting enables automatic update of MPD's database when files in 

doc/protocol.xml

@@ -202,6 +202,25 @@
         omitted, then the maximum possible value is assumed.
       </para>
     </section>
+
+    <section id="tags">
+      <title>Tags</title>
+
+      <para>
+        The following tags are supported by
+        <application>MPD</application>:
+      </para>
+
+      <xi:include href="include/tags.xml"
+                  xmlns:xi="http://www.w3.org/2001/XInclude"/>
+
+      <para>
+        There can be multiple values for some of these tags.  For
+        example, <application>MPD</application> may return multiple
+        lines with a <varname>performer</varname> tag.  A tag value is
+        a UTF-8 string.
+      </para>
+    </section>
   </chapter>
 
   <chapter id="recipes">

doc/user.xml

@@ -1298,6 +1298,19 @@ database {
       </para>
     </section>
 
+    <section id="tags">
+      <title>Metadata</title>
+
+      <para>
+        When scanning or playing a song,
+        <application>MPD</application> parses its metadata.  The
+        following tags are supported:
+      </para>
+
+      <xi:include href="include/tags.xml"
+                  xmlns:xi="http://www.w3.org/2001/XInclude"/>
+    </section>
+
     <section id="queue">
       <title>The queue</title>