Audit missing category declarations about xhp-lib HOT 4 CLOSED

You can assign me to this issue.
I've read enough html and svg spec to make it feel sorta pleasant.
Is this a blocker for v4 with a dead line? Or could I do this when I know I'll be having a lot of time in early August?

from xhp-lib.

Given it's pre-existing, and most likely adding things rather than removing, it should be backwards compatible (or BC-enough... ). No need for this to be in .0

from xhp-lib.

Speaking of which, now that we're using interfaces, we could bake in these rules via extension.
I'd much rather say.

interface Phrase {
  require implements Flow;
}

But that is reserved for traits.

from xhp-lib.

Anything other than Category\Meta implies Category\Flow.
Category\Embedded implies Category\Phrasing.

from xhp-lib.