+U: setatt attribute1{+|-} [attribute2{+|-}...] pattern
+
+H: Set ('+') or unset ('-') the given attributes for all audio files matching
+H: pattern. Example:
+H:
+H: sa rock+ punk+ classic- '*foo.mp3'
+H:
+H: sets the 'rock' and the 'punk' attribute but unsets the 'classic'
+H: attribute of all files ending with 'foo.mp3'.