code: function findFocus( id, returnProperty ) {
          var tabs = $G( id ).children,
                  property;
          for ( var i = 0, ci; ci = tabs[i++]; ) {
              if ( ci.className=="focus" ) {
                  property = ci.getAttribute( returnProperty );
                  break;
              }
          }
          return property;
      }
docs: 找到id下具有focus类的节点并返回该节点下的某个属性
  @param id
  @param returnProperty