Looks pretty good. Not sure how I feel about including JSON as type of embedded content, though. I've used something vaguely similar in the distant past, but i

Looks pretty good. Not sure how I feel about including JSON as type of embedded content, though. I've used something vaguely similar in the distant past, but it was strictly internal for my hobby projects and mostly resembled lisp with square brackets. It was way more primitive, but the parser (lexer, really) fit into two blocks of code. All the fancy stuff was done within DOM.