Search a Ns registered under a given name space for a
          document. recurse on the parents until it finds the defined
          namespace or return None otherwise. @nameSpace can be None,
          this is a search for the default namespace. We don't allow
          to cross entities boundaries. If you don't declare the
          namespace within those you will be in troubles !!! A
           warning is generated to cover this case.

def searchNs(self, node, nameSpace):
        """Search a Ns registered under a given name space for a
          document. recurse on the parents until it finds the defined
          namespace or return None otherwise. @nameSpace can be None,
          this is a search for the default namespace. We don't allow
          to cross entities boundaries. If you don't declare the
          namespace within those you will be in troubles !!! A
           warning is generated to cover this case. """
        if node is None: node__o = None
        else: node__o = node._o
        ret = libxml2mod.xmlSearchNs(self._o, node__o, nameSpace)
        if ret is None:raise treeError('xmlSearchNs() failed')
        __tmp = xmlNs(_obj=ret)
        return __tmp