code: function(e, numbersOnly) {
              var command = this._getCommand(e);
              switch (command) {
                  case 6: // return
                  case 5: // special char
                  case 1: // number
                      break;
                  case 2: // hex char (a-f)
                      if (numbersOnly !== true) {
                          break;
                      }
  
                      // fallthrough is intentional
  
                  default: // prevent alpha and punctuation
                      Event.stopEvent(e);
                      return false;
              }
          }
docs: Allows numbers and special chars, and by default allows a-f.
  Used for the hex field keypress handler.
  @method _hexOnly
  @param e {Event} the event
  @param numbersOnly omits a-f if set to true
  @protected
  @return {boolean} false if we are canceling the event