code: public Actions keyDown(CharSequence key) {
      if (isBuildingActions()) {
        action.addAction(new KeyDownAction(jsonKeyboard, jsonMouse, asKeys(key)));
      }
      return addKeyAction(key, codePoint -> tick(defaultKeyboard.createKeyDown(codePoint)));
    }
docs: Performs a modifier key press. Does not release the modifier key - subsequent interactions
  may assume it's kept pressed.
  Note that the modifier key is <b>never</b> released implicitly - either
  <i>keyUp(theKey)</i> or <i>sendKeys(Keys.NULL)</i>
  must be called to release the modifier.
  @param key Either {@link Keys#SHIFT}, {@link Keys#ALT} or {@link Keys#CONTROL}. If the
  provided key is none of those, {@link IllegalArgumentException} is thrown.
  @return A self reference.