ConstList which lyrics sources exist for path, including empty tags or files.
A non-empty filename selects one file next to the audio file.
Read a track's lyrics: embedded tags first, then sidecar files next to
the audio file. Omit path for the playing track; with nothing playing
the host answers NO_ACTIVE_ITEM. A non-empty filename replaces the
automatic file candidates; use source: 'file' to skip embedded tags.
Save lyrics to one or more targets. The host takes target as an array;
a single string is sent as a one-element array. With one target the
response describes that write, with several each outcome is keyed under
results. all writes the file and embedded targets. A non-empty
filename selects the output file without applying format.
lyrics— lyrics fetch / save namespace.