See the corresponding xkeyboard-config issue and libxkbfile issue.

The idea would be to be able to have a suffix per option, such as it applies only to some layout indexes.

Some preliminary ideas:

• , cannot be used as a suffix delimeter, as it is the option separator.
• : should not be used as a suffix delimeter, e.g. eurosign:e:2, because it is ambiguous.
• @ seems an interesting candidate; it clashes with nothing currently. E.g.: eurosign:e@2
• We should embrace Modern rules #362 and introduce @all, @first, etc. as well.
• We need DE devs to be implied, if we want a proper UI to be developed.
• There should be none or only very limited breakage, as it is the “compiled” keymap that is shared by the compositor with the apps, not the RMLVO values.