CSSPseudoElement IDL design

Hi all!

I'm going to work on improving CSSPseudoElement IDL interface design.
I came up with a public doc to list open questions at
https://github.com/danielsakhapov/CSSPseudoElementDoc

And opened an issue for each question mentioned in the doc.
https://github.com/w3c/csswg-drafts/issues/12158
https://github.com/w3c/csswg-drafts/issues/12159
https://github.com/w3c/csswg-drafts/issues/12160
https://github.com/w3c/csswg-drafts/issues/12161
https://github.com/w3c/csswg-drafts/issues/12162
https://github.com/w3c/csswg-drafts/issues/12163

Some of them I feel are quite easy to resolve, so, please, have a look and
leave a comment!

Thanks, Daniil.