public function keyDown($xpath, $char, $modifier = null) {
    $element = $this->findElement($xpath, 1);
    $key = $this->normalizeCharForKeyEvent($char);
    $modifier = $this->keyEventModifierControl($modifier);
    return $this->browser->keyEvent($element["page_id"], $element["ids"][0], "keydown", $key, $modifier);
  }