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> Some time later on, my brain fully exploded when I realised that there is no clean layered separation possible (at least that I could envisage) that would still give you all the features of full-on SGML.
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> Some time later on, I concluded that this is inevitably true in any powerful text processing system because semantics - real semantics - is on great big hermeneutic circle.
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XML could have achieved far better separation if it had chosen. The intertwingling of the physical and logical layers caused by the rule that elements must be well-balanced within entities is a quite unnecessary constraint on implementation modularity; the interactions between entity expansion and syntactic parsing within DTDs are even worse. I don't think it's at all true that these complications are inevitable.
Michael Kay
Saxonica
