How could a browser "automatically" know what changes I'm going to make to the DOM in a dynamic web app? Having the browser try to guess what transitions will b

How could a browser "automatically" know what changes I'm going to make to the DOM in a dynamic web app? Having the browser try to guess what transitions will be needed in the near future based on "related" selectors sounds way more hacky than a straightforward property that declares it. As the article notes, for all but trivial examples, these are likely to be added via Javascript. The static CSS file with ":hover" and ":active" was jsut an example.