code: function pickValue( ref, node, success, complete ) {
  
          if ( !ref ) {
              console.error('pickValue !ref return');
              return;
          }
  
          var events = {};
          $$.defineEvent( events );
  
          events.eventListener({
              // limit: 1,
              self: this,
              action: 'success',
              listen: success
          });
  
          events.eventListener({
              self: this,
              action: 'complete',
              listen: complete
          });
  
          ref.exec({ node: node }, events );
      }
docs: @private
  @param  {*}               ref
  @param  {*}               node
  @return {*}
  
  @memberOf util.path