title: Does PHP have a convention for describing Promise returns in function docblock
body: <p>I just wrote a function like this </p>
  
  <pre><code>  /**
     * Send an asynchronous GET request
     *
     * @param string $url
     * @param array  $options
     *
     * @return \React\Promise\ExtendedPromiseInterface
     */
    public function getAsync( $url, array $options = [] );
  </code></pre>
  
  <p>but when making docblock, I realized that <code>@return \React\Promise\ExtendedPromiseInterface</code> is very generic and doesn't really help client understand what returns are to be expected in case of rejection or fulfillment. </p>
  
  <p>Is there some established convention for documenting which values or exception are expected as a result of this function so that the client could chain on this function by looking at the interface only?</p>