title: Mink/behat iframe without id/name
body: <p>I have to verify text/messages inside an iframe wihout a name/id. After exploring, I found out that solution to add id/name and use switchToIFrame(id/name). How can I set id/name to a node element in mink? SetAttribute() is not a supported method in nodelement and setValue()  is not supported for a frame.</p>
  
  <pre><code>&lt;html&gt;
    &lt;body&gt;
      &lt;div class="div1"&gt;
      &lt;iframe class="xyz"&gt;
        &lt;!DOCTYPE html&gt;
        &lt;html&gt;
          &lt;body&gt;
            &lt;div class="frame"&gt;&lt;/div&gt;
            &lt;p&gt;The paragraph1&lt;/p&gt;
          &lt;/body&gt;
         &lt;/html&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>My context file is </p>
  
  <pre><code>public function iShouldSeeDescription($arg1)
  {
      $expected = "The paragraph1";
      $iframe=$this-&gt;getSession ()-&gt;getPage ()-&gt;find ( 'xpath', '//div[contains(@class,"div1")]/iframe[contains(@class,"xyz")]');
      $iframe-&gt;setAttribute('id', 'iframe_id');
      $iframeId = $iframe-&gt;getAttribute('id');
      $this-&gt;getSession()-&gt;switchToIframe("$iframeId");
      $actual = $this-&gt;getSession()-&gt;getPage()-&gt;find('xpath', '//div[@class="frame"]/p[1]');
      if ($actual === null) {
          throw new \InvalidArgumentException ( sprintf ( 'null:%s', $arg1 ) );
      }
      if (!($actual === $expected)) {
          throw new \InvalidArgumentException ( sprintf ( 'The Acutal description:%s and expected description:%s did not match ', $actual, $expected ) );
      }
  
  }
  </code></pre>