Thanks for the patch.

I think this is probably *not* desirable in this form.  As a side effect of writexml(), this fixes up tagNames and attributes of elements in the document.  DOM Level 3 Load and Save made the opposite decision:  "The XML data is written to a string or an output stream. Any changes or fixups made during the serialization affect only the serialized data. The Document object and its children are never altered by the serialization operation."  -- http://www.w3.org/TR/2004/REC-DOM-Level-3-LS-20040407/load-save.html#LS-LSSerializer (first paragraph)  I think that is the right approach.

The new method Element.normalizeNamespace() isn't really a DOM method, though the appendix sort of makes it look that way.

Incomplete - no doc patch.  (I think there's also a bug in the line added to Document.writexml()-- can't Documents have children that aren't Elements?)