XML::LibXML XPath fails to find xmlns:xml="http://www.w3.org/XML/1998/namespace"

Hi,

I have found a strange behavior of XML::LibXML when handling the results 
of an XPath search that includes namespaces using the prefix 'xml'.

If a document defines the following namespace:  
xmlns:xml="http://www.w3.org/XML/1998/namespace" then the XPath 
expression '//namespace::*' will not return that namespace. I have 
attached a test case that shows the problem. The test may seem strange 
as there are more namespaces returned than declared but this is what 
xmllint --shell returns!

I think that this "bug" is a border line case as the prefix 'xml' is 
reserved in the XML specification. Although, I think that it should be 
fine to use xmlns:xml="http://www.w3.org/XML/1998/namespace" in a 
document [See http://www.stylusstudio.com/xmldev/200201/post91720.html].

I tried to use xmllint --shell and a sample C program using the XPath 
API of libxml and they both work fine. So I made some investigation and 
found out that the XS method XML::LibXML::Node::_findnodes() is removing 
the nodes involuntarily through this code:

  if (tnode->type == XML_NAMESPACE_DECL) {
    xmlNsPtr newns = xmlCopyNamespace((xmlNsPtr)tnode);
    if ( newns != NULL ) {
      element = NEWSV(0,0);
      cls = PmmNodeTypeName( tnode );
      element = sv_setref_pv( element,
        (const char *)cls,
        newns
      );
    }
    else {
      continue;
    }
  }

The call to xmlCopyNamespace() is the source of the problem. 
xmlCopyNamespace() uses xmlNewNs() to create a new node, but xmlNewNs() 
has the following assertion:

  if ((prefix != NULL) && (xmlStrEqual(prefix, BAD_CAST "xml")))
    return(NULL);

That's why findnodes() is discarding some results, xmlNewNs() refuses to 
create a namespace node having the prefix "xml".

PS: The same should be true for XML::LibXML::XPathContext::_findnodes().

Emmanuel Rodriguez.

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