private function _extractDomain(\Twig_Node $node)
	{
		// must be a filter node
		if (!$node instanceof \Twig_Node_Expression_Filter) {
			return null;
		}
		// is a trans filter
		if ($node->getNode('filter')->getAttribute('value') == 'trans') {
			if ($node->getNode('arguments')->hasNode(1)) {
				return $node->getNode('arguments')
					->getNode(1)
					->getAttribute('value');
			} else {
				return $this->defaultDomain;
			}
		}
		
		return $this->_extractDomain($node->getNode('node'));
	}