If you decided you don't want that, you could come up with a XML document format that doesn't allow nested formatting blocks. So your point seems awfully moot.

If you decided you don't want that, you could come up with a XML document format that doesn't allow nested formatting blocks. So your point seems awfully moot. In fact, even with HTML you could remove all the nesting from formatting blocks on load and either put them back on save or leave it flat (assuming you use CSS and not semantic style tags).