public final XSComponent selectSingle(XSSchemaSet contextNode){
  Iterator<XSComponent> r=select(contextNode.iterateSchema());
  if (r.hasNext())   return r.next();
  return null;
}

public final XSComponent selectSingle ( XSSchemaSet contextNode ) { Iterator < XSComponent > r = select ( contextNode . iterateSchema ( ) ) ; if ( r . hasNext ( ) ) return r . next ( ) ; return null ; }
evaluates the scd against the whole schema set and returns the matched node .
