I think it's excellent that HTML5 completely specifies the parsing in a very clear, and most backwards-compatible way; judging by what the big browser vendors have been doing, they seem to be following it. (It also gives a nice starting point that makes it easier for anyone to write their own parser, and have it behave the same as any other mainstream browser - and having the possibility of making more browsers available, with the same standard parsing behaviour, is a good thing.)