code: public Actions keyDown(WebElement target, CharSequence key) {
      if (isBuildingActions()) {
        action.addAction(new KeyDownAction(jsonKeyboard, jsonMouse, (Locatable) target, asKeys(key)));
      }
      return focusInTicks(target)
          .addKeyAction(key, codepoint -> tick(defaultKeyboard.createKeyDown(codepoint)));
    }
docs: Performs a modifier key press after focusing on an element. Equivalent to:
  <i>Actions.click(element).sendKeys(theKey);</i>
  @see #keyDown(CharSequence)
  
  @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.
  @param target WebElement to perform the action
  @return A self reference.