code: public function getValue(ApistMethod $method, Crawler $rootNode = null)
  	{
  		if (is_null($rootNode))
  		{
  			$rootNode = $method->getCrawler();
  		}
  		$result = $rootNode->filter($this->selector);
  		return $this->applyResultCallbackChain($result, $method);
  	}
docs: Get value from content by css selector
  
  @param ApistMethod $method
  @param Crawler $rootNode
  @return array|null|string|Crawler