1- Correctness. It's still possible to generate bad XML. Especially in
2	safe mode, checks on processing instructions, comments and DOCTYPE
3	declarations should be rigorously matched against the spec.
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5- Control over presentation. How much is too much? Entities vs. CDATA,
6	placement of namespace declarations, whitespace. How much control
7	should the user be given?
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9- Performance. Reducing the use of closures may speed things up, and
10	benchmarking would show whether or not it's worth it.
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