It means that the song has been recently inserted.
It means that the song has a musical score for a secondary instrument.
It means that in addition to read the song we can hear it.
It means that in addition to this version of the song, an old version of it is
also available (now for its lyrics, now for its music).
It means that there is information about the song
The background colours of the songs mean:
Songs for the Anaphora