+=head1 FILESYSTEM LAYOUT
+
+A path in the filesystem consists of a tag query expression, followed
+by directories containing the matching files, arranged by artist and
+album.
+
+Example paths:
+
+ /krautrock/AND/year/1971/
+ /krautrock/AND/year/1971/Can
+ /krautrock/AND/year/1971/Can/Tago Mago/01-Paperhouse.mp3
+ /krautrock/AND/year/1971/Can/NOALBUM/Can - Oh Yeah (Live).mp3
+ /krautrock/AND/year/1971/Can/TRACKS/01-Paperhouse.mp3
+ /krautrock/AND/year/1971/Can/TRACKS/Can - Oh Yeah (Live).mp3
+ /krautrock/AND/year/1971/NOARTIST/unknown-track.mp3
+ /krautrock/AND/year/1971/TRACKS/01-Paperhouse.mp3
+
+id3fs supports OR, AND and NOT. NOT has the highest precedence,
+followed by AND, so F<foo/OR/NOT/bar/AND/baz> is parsed as
+(foo OR ((NOT bar) AND baz)).
+
+=head2 Tags
+
+Tags are extracted from the B<genre> tag of audio files with
+L<id3fs-index(1)>.
+
+Within the genre frame/comment, tags are separated by commas.
+
+Tags can have values, separated by a slash, eg I<metal/thrash>,
+I<rating/5>. Certain special tags are automatically filled in from
+other file metadata.
+
+=head2 Special Tags
+
+The following tags are automatically derived from other metadata in
+the audio files:
+
+=over 4
+
+=item B<year>
+
+Extracted from the B<year> or B<DATE> tag. If not found defaults to
+B<year/UNKNOWN>.
+
+=item B<decade>
+
+Also extracted from the B<year> or B<DATE> tag. If not found
+defaults to B<decade/UNKNOWN>.
+
+=item B<v1genre>
+
+If a mp3 file has an ID3V1.1 genre tag, its value is assigned to
+v1genre.
+
+=item B<audiotype>
+
+Type of audio file (mp3, ogg, flac). Always set.
+
+=back
+
+=head2 Special Directories
+
+=over 4