[Selectors4] Define Selectors in terms of the DOM

I think Selectors need to be defined in terms of the DOM. The DOM is the  
tree model Selectors work upon in all implementations, and it is the tree  
model the languages we care about are defined in. And if we want Selectors  
to work for other tree models we could just state they have to be  
equivalent to the DOM. That would work. But hand-waving about the tree  
model Selectors work against should stop I think.


-- 
Anne van Kesteren
http://annevankesteren.nl/