public function getContextsByRef( $refs )
	{
		$contexts = array();

		if ( is_array( $refs ) )
		foreach ( $refs as $ref )
		{
			if ( ! isset( $this->contexts[ $ref ] ) ) continue;
			$contexts[ $ref ] = $this->contexts[ $ref ];
		}

		return new ContextsFilter( $this->instance, $contexts );
	}