[csswg-drafts] [css-pseudo-4] Should Element.pseudo("unknown") be an error or return null? (#3603)

fantasai has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-pseudo-4] Should Element.pseudo("unknown") be an error or return null? ==
We resolved to have an Element.pseudo(type) interface that returns a CSSPseudoElement. What happens if someone passes a type that isn't known to the implementation? Do we treat it as non-existent or do we throw an error?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3603 using your GitHub account