/*
 * 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;
}