code: protected function getTypeUrl($class, $method)
      {
          if (strpos($class, 'yii\\') !== 0) {
              return null;
          }
  
          $page = $this->htmlEncode(strtolower(str_replace('\\', '-', $class)));
          $url = "http://www.yiiframework.com/doc-2.0/$page.html";
          if ($method) {
              $url .= "#$method()-detail";
          }
  
          return $url;
      }
docs: Returns the informational link URL for a given PHP type/class.
  @param string $class the type or class name.
  @param string|null $method the method name.
  @return string|null the informational link URL.
  @see addTypeLinks()