public function setEngine($engine)
	{
		// if param given as an object
		if ($engine instanceof Dwoo) {
			$this->_engine = $engine;
		}
		//
		elseif (is_subclass_of($engine, 'Dwoo') || 'Dwoo' === $engine) {
			$this->_engine = new $engine();
		}
		else {
			throw new Dwoo_Exception("Custom engine must be a subclass of Dwoo");
		}
	}