A while back I said that packaging in XML is currently Atom's biggest technical headache. Ken McLeod is laying out why this is so on atom-syntax: Once we have reduced Atom's inlinable content types to non-schizophrenic portions, we're basically left with XML characters and XML fragments. XML is not architected for carrying non-XML content and this seems to be generally insoluble - insofar as whatever solution one comes up with will always be inferior to MIME....