code: function( keyCode ) {
  			if ( typeof keyCode != 'number' ) {
  				return this.stack.length - 1; // Last index or -1.
  			} else {
  				var i = this.stack.length;
  				while ( i-- ) {
  					if ( this.stack[ i ].keyCode == keyCode ) {
  						return i;
  					}
  				}
  				return -1;
  			}
  		}
docs: Returns the index of the last registered `keyCode` in the stack.
  If no `keyCode` is provided, then the function will return the index of the last item.
  If an item is not found, it will return `-1`.
  
  @param {Number} [keyCode]
  @returns {Number}