I curious - why do you think this would make serialization difficult?  The attribute would be in the DOM in its original form, so when serializing wouldn't it just get emitted in its original form?

Bjoern Hoehrmann wrote:
* Henri Sivonen wrote:
  
The public DOM API is required to throw when setting an attribute  
whose namespace is null and whose local name is "xmlns:foo":
    

That is only the case for the namespace-aware methods; you can use the
DOM Level 1 methods to create such attributes. Obviously this results
in difficulties if you try, say, to serialize the document.
  

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