Now that we have the keymap format v2 and that it is the default, we should probably make serializing of multiple actions per level fallback to VoidAction() in format v1, while still enabling its parsing & handling.

This would not be necessary if xkbcomp could ignore those, but I am not sure I will have time to implement it. This is also an issue for older xkbcommon shipped in e.g. flatpaks.

For consistency, we could do the same with multiple keysyms per levels, so that v1 has a better compatibility. On the other hand, this latter feature is already ignored by xkbcomp and has be around for quite a time, so… let’s keep it?