The comment tag currently supports an optional language and description in the form of "comment:{lang}:{description}". As both are optional and historically also "comment:{description}" was supported this can lead to ambiguity, as e.g. reported in PICARD-2468.

The proposal is to make the colons mandatory, even if language is empty. So only this syntax would be valid:

1. Only comment without language and descrpition: comment
2. Comment with both language and description: comment:eng:sometext
3. Comment with only language: comment:eng
4. Comment with empty language but description set: comment::sometext

The 4th case is new. It avoids confusion between case 3 and 4, which is currently in some cases indistinguishable.

As also the lyrcis tag should have the language (PICARD-1877) the same logic should apply there.

This is a breaking change, so this is definitely for Picard 3 and we should consider ways to avoid friction.