This matches Gecko and WebKit. The disabled condition was added to the spec in 9985973 but not implemented uniformly. As discussed in #6635, it doesn't work very well and is inconsistent with other similar pseudo-classes, like :hover.

This also removes the consideration of <link> elements with href="" attributes, since they no longer have activation behavior as of 1e0ee7f. And it updates the definitions of both :active and :hover to be based on the latest Selectors spec, which notably includes the ancestor condition over the flat tree at the CSS layer, instead of having HTML handle that.

There remains some lack of interop around elements such as <input type=radio> which have activation behavior but are not on the list of elements for which "in a formal activation state" is considered. #6635 stays open to track that case.