code: function _recordKey(key) {
          var i;
  
          // one-off implementation of Array.indexOf, since IE6-9 don't support it
          for (i = 0; i < _currentRecordedKeys.length; ++i) {
              if (_currentRecordedKeys[i] === key) {
                  return;
              }
          }
  
          _currentRecordedKeys.push(key);
  
          if (key.length === 1) {
              _recordedCharacterKey = true;
          }
      }
docs: marks a character key as held down while recording a sequence
  
  @param {string} key
  @returns void