[xml] xpath expression and namespaces

[Aleksey Sanin <aleksey aleksey com>]

Daniel,

I have a strange problem with XPath expressions + namespaces and I would
like to get your opinion on this. Suppose we have following XML document:

   <foo:Root xmlns:bar="http://example.org/bar";
           xmlns:baz="http://example.org/baz"; 
xmlns:foo="http://example.org/foo";
           xmlns="http://example.org/";
           xml:lang="en-ie">
       <bar:Something>
           <foo:Something>
               <bar:Something>
                   <foo:Something>
                       <baz:Something />
                   </foo:Something>
               </bar:Something>
           </foo:Something>
       </bar:Something>
   </foo:Root>

and the following XPath expression (in XMLDSig notation):

   <XPath xmlns:bar="http://example.org/bar"; >
       (//. | //@* | //namespace::*)
       [
        ancestor-or-self::bar:Something  and
           (self::text()  or (namespace-uri() != "")  or
           (string(self::node()) = namespace-uri(parent::node())))
       ]
   </XPath>

The expectation is that this XPath expression will select the 
bar:Something subtree,
but only includes namespace nodes that are directly used by their parent 
element.
However, the LibXML results looks as follows (using xmlDebugDumpNode()):

ELEMENT bar:Something
 TEXT
   content=
 ELEMENT foo:Something
   TEXT
     content=
   ELEMENT bar:Something
     TEXT
       content=
     ELEMENT foo:Something
       TEXT
         content=
       ELEMENT baz:Something
       TEXT
         content=
     TEXT
       content=
   TEXT
     content=
 TEXT
   content=
TEXT
 content=
ELEMENT foo:Something
 TEXT
   content=
 ELEMENT bar:Something
   TEXT
     content=
   ELEMENT foo:Something
     TEXT
       content=
     ELEMENT baz:Something
     TEXT
       content=
   TEXT
     content=
 TEXT
   content=
TEXT
 content=
ELEMENT bar:Something
 TEXT
   content=
 ELEMENT foo:Something
   TEXT
     content=
   ELEMENT baz:Something
   TEXT
     content=
 TEXT
   content=
TEXT
 content=
ELEMENT foo:Something
 TEXT
   content=
 ELEMENT baz:Something
 TEXT
   content=
TEXT
 content=
ELEMENT baz:Something
TEXT
 content=
TEXT
 content=
TEXT
 content=
TEXT
 content=

As you can see, we have nodes instead of namespace in the result nodes 
set. I looked at
the xpath.c file and found following comment (that probably explains the 
above result):

   /**
    * xmlXPathNodeSetDupNs:
    * @node:  the parent node of the namespace XPath node
    * @ns:  the libxml namespace declaration node.
    *
    * Namespace node in libxml don't match the XPath semantic. In a 
node set
    * the namespace nodes are duplicated and the next pointer is set to the
    * parent node in the XPath semantic.
    *
    * Returns the newly created object.
    */

My question is: what was the reason for this special namespace nodes 
processing and can
we process namespace nodes in the same way as all other nodes in xpath 
evaluation?


Aleksey.