Add support for vendor-prefixed values

[hediyi]

They're rare but they actually exist (see the specs for some examples), can't say there won't be more, hence the PR 😉

[winstliu]

Why weren't the (xx) ones moved to be reverse-alphabetical?

[hediyi]

Coz I sorted them with something like

s.split('|').sort { |a, b| b <=> a }.join('|')

and the first char ( is "smaller" than letters, so they ended up at the end.

The main reason I expanded the nested alternations is to get rid of the |s in them so they don't get in the way of the script above (which can be used every time you add new values). (xx?-)?small doesn't contain a | and I got lazy 😆

That a problem?