Question on canonical XML (incl/excl)

Hi all,

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REC-xml-c14n-20010315#ProcessingModel states:

   "... if the first node is not the default namespace node
    (a node with no namespace URI and no local name)"

Why does the default namespace node have no namespace URI and no local name? I thought that xmlns="http://foo" has a namespace URI of "http://www.w3.org/2000/xmlns/" and a local name of "xmlns" and no prefix?

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REC-xml-exc-c14n-20020718.html#sec-Specification states:

3.3.3:

   "A namespace node N with a prefix that does not appear in
    the InclusiveNamespaces PrefixList is rendered if
    ...
    (3) the prefix has not yet been rendered by any output ancestor"

How do you implement this? Do you have a stack where you remember all already rendered prefixes?

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Christian