code: function (p_oEvent) {
          
              var oTarget = Event.getTarget(p_oEvent),
                  nCharCode = Event.getCharCode(p_oEvent),
                  sId = oTarget.parentNode.parentNode.id,
                  oButton = m_oButtons[sId],
                  nIndex = -1;
          
          
              if (nCharCode == 37 || nCharCode == 38) {
          
                  nIndex = (oButton.index === 0) ? 
                              (this._buttons.length - 1) : (oButton.index - 1);
              
              }
              else if (nCharCode == 39 || nCharCode == 40) {
          
                  nIndex = (oButton.index === (this._buttons.length - 1)) ? 
                              0 : (oButton.index + 1);
          
              }
          
          
              if (nIndex > -1) {
          
                  this.check(nIndex);
                  this.getButton(nIndex).focus();
              
              }        
          
          }
docs: Protected event handlers 
  @method _onKeyDown
  @description "keydown" event handler for the button group.
  @protected
  @param {Event} p_oEvent Object representing the DOM event object
  passed back by the event utility (YAHOO.util.Event).