code: function isShiftKeyOnly(event) {
    return (
      !event.altKey &&
        !(event.metaKey || event.ctrlKey) &&
        event.shiftKey);
  }
docs: Same as `ol.events.condition.shiftKeyOnly`.
  @param {JQueryEventObject} event Event.
  @return {boolean} True if only the shift key is pressed.
  @private