If $unset is called, the tag will not be changed when Picard saves the file, but that value is no longer available to scripting.  For example, if the file's composer is "B & A" (single value), MusicBrainz has the composer as "A; B" (2 values), and we call $unset(composer), then %composer% will now return empty.  It would be very useful if %composer% would instead return "B & A" from the file at that point so that we can compare our local value against the server's value.

Example taggerscript:

$setmulti(_serverComposer,$join(%composer%,	),	)
$unset(composer)
$set(_localComposer,%composer%)