public function getAllElementClassContentClassnames()
    {
        $classnames = array_filter(
            $this->getAllClassContentClassnames(),
            function ($classname) {
                return false !== strpos(
                    $classname,
                    AbstractClassContent::CLASSCONTENT_BASE_NAMESPACE.'Element\\'
                );
            }
        );

        $classnames[] = AbstractClassContent::CLASSCONTENT_BASE_NAMESPACE.'ContentSet';

        return $classnames;
    }