title: Escape quotes in an iframe srcdoc value
body: <p>According to the <a href="http://www.w3.org/TR/html5/embedded-content-0.html#attr-iframe-srcdoc">spec</a> quotes have to be escaped, i.e. instead of:</p>
  
  <pre><code>&lt;iframe seamless sandbox srcdoc="&lt;p&gt;Yeah, you can see it &lt;a href="/gallery?mode=cover&amp;amp;page=1"&gt;in my gallery&lt;/a&gt;."&gt;&lt;/iframe&gt;
  </code></pre>
  
  <p><br>we should use:</p>
  
  <pre><code>&lt;iframe seamless sandbox srcdoc="&lt;p&gt;Yeah, you can see it &lt;a href=&amp;quot;/gallery?mode=cover&amp;amp;amp;page=1&amp;quot;&gt;in my gallery&lt;/a&gt;."&gt;&lt;/iframe&gt;
  </code></pre>
  
  <p><br>But isn't it OK to simply use single quotes in the above example:</p>
  
  <pre><code>&lt;iframe seamless sandbox srcdoc="&lt;p&gt;Yeah, you can see it &lt;a href='/gallery?mode=cover&amp;amp;page=1'&gt;in my gallery&lt;/a&gt;."&gt;&lt;/iframe&gt;
  </code></pre>