Sure, but the major text is still "write once" -- you can only add specially designated information to a read-only core. As this article shows, a trivial opera

Sure, but the major text is still "write once" -- you can only add specially designated information to a read-only core. As this article shows, a trivial operation on the core text, like "remove a blank page", is still very hard and pretty easy to get wrong. I think having general Turing-complete power in a document format is a horrible idea. It's a pity we ended up with it. Something like OpenOffice's presentations ("odp") is also a single file which is layed out per page, and can be annotated, commented, approved, edited and so on, while not being Turing-complete.