/**
* Adds a visitor.
*
* @param Twig_NodeVisitorInterface $visitor A Twig_NodeVisitorInterface instance
*/
public function addVisitor(Twig_NodeVisitorInterface $visitor)
{
if (!isset($this->visitors[$visitor->getPriority()])) {
$this->visitors[$visitor->getPriority()] = array();
}
$this->visitors[$visitor->getPriority()][] = $visitor;
}