Should subtags be accepted?

[justingrant]

Should locale subtags like '-hc-h12' be accepted with this locale?

Some subtags may be contrary to the intent of this proposal, like changing the numbering system. If subtags are accepted, then the proposal should define which subtags are supported and what the bahavior should be if an unsupported subtag is provided.

[hsivonen]

I think Intl.Collator should accept -u-co- for und. In particular, -u-co-emoji is only supported with root, and this becomes clearer if und-u-co-emoji works. It seems like a bad idea to teach en-u-co-emoji or fr-u-co-emoji, which work only incidentally, because these languages don't have a language-specific tailoring.