code: function(event) {
  			var inst = plugin._getInst((event.data && event.data.elem) || event.target);
  			if (!$.isEmptyObject(inst) && inst.options.constrainInput) {
  				var ch = String.fromCharCode(event.keyCode || event.charCode);
  				var allowedChars = plugin._allowedChars(inst);
  				return (event.metaKey || inst.ctrlKey || ch < ' ' ||
  					!allowedChars || allowedChars.indexOf(ch) > -1);
  			}
  			return true;
  		}
docs: Filter keystrokes in the datepicker.
  @memberof CalendarsPicker
  @private
  @param event {KeyEvent} The keystroke.
  @return {boolean} <code>true</code> if allowed, <code>false</code> if not allowed.