/**
  * Add some HTML to be cached.
  * This is done by providing a callback function that should
  * return the HTML to be added. It will only be called if the
  * item is not in the cache yet or when the cache has been invalidated.
  *
  * @since 1.20
  *
  * @param callable $computeFunction
  * @param array $args
  * @param string|null $key
  */
 public function addCachedHTML($computeFunction, $args = array(), $key = null)
 {
     $this->getOutput()->addHTML($this->cacheHelper->getCachedValue($computeFunction, $args, $key));
 }