It's way too complex and hard to use. Either have stricter definitions or fewer definitions.
are duplicates allowed? No.
what's the exact behavior of /xx/ and [/xx/]? /xx/ is preferred and indicates that it represents a known list of arbitrary length. This is weird.
Alternatively:
It's way too complex and hard to use. Either have stricter definitions or fewer definitions.
/xx/and[/xx/]?/xx/ is preferred and indicates that it represents a known list of arbitrary length. This is weird. Alternatively: