Cross-browser Standards\ Entries need to work equally well in IE10's latest platform preview, and latest versions of Firefox and a Webkit browser of your choice (Chrome or Safari).
It doesn't bother me that much there is not Opera in the list. Opera is yet another specific browser. Nope. It bothers me that they do not encourage full plain interoperability. I would have been appealed with:
\ Only use technologies implemented everywhere in browser released versions check caniuse.com/\
This indeed will exclude a lot of shiny things including some of Opera, but they will be a closer of a Web developer reality.