css selection pseudo-element animation

I wrote Tab Atkins and he answers:

In general, most browsers have trouble running animations on pseudo-elements. We're gradually fixing these issues, but it's slow work, because pseudo-elements are pretty complicated to handle in the browser.

On top of that, the ::selection pseudo-element is the most complicated pseudo-element in all of CSS. It's so complicated, we explicitly undefined it in our specs until we figure out how to actually specify it in a way that works well.

Most of what I see on animation is:

Applies To: all elements, ::before and ::after pseudo-elements

Which suggests not other pseudo-elements or states?