    /*
     * call-seq:
     *  namespaced_key?(attribute, namespace)
     *
     * Returns true if +attribute+ is set with +namespace+
     */
    static VALUE namespaced_key_eh(VALUE self, VALUE attribute, VALUE namespace)
    {
      xmlNodePtr node;
      Data_Get_Struct(self, xmlNode, node);
      if(xmlHasNsProp(node, (xmlChar *)StringValuePtr(attribute),
            NIL_P(namespace) ? NULL : (xmlChar *)StringValuePtr(namespace)))
        return Qtrue;
      return Qfalse;
    }