title: "This interface to HTML5 document checking is deprecated"
body: <p>While doing a project I was checking it for W3C errors (using <strong><a href="https://addons.mozilla.org/en-us/firefox/addon/html-validator/" rel="nofollow">html validator</a></strong> plug-in for Firefox), and in the process I found a warning that never showed up to me ever before.</p>
  
  <blockquote>
    <p>"<strong><em>Warning:</strong> This interface to HTML5 document checking is deprecated</em>"</p>
  </blockquote>
  
  <ul>
  <li>So, first thing came up to my mind, "<em>let me Google this</em>" and see what information I could find about this warning, but I didn't get anything.</li>
  <li>Tried another approach, which was going to the actual <strong><a href="https://validator.w3.org" rel="nofollow">W3C Validator</a></strong> and see the outcome.But, I was given the same warning (shown below), but this time it was pointing me to a different link to <strong>check again</strong>, which I did, but I couldn't understand why I had to check in <strong><a href="https://validator.w3.org/nu/" rel="nofollow">W3C validator NU</a></strong> and not in <strong><a href="https://validator.w3.org" rel="nofollow">W3C validator original</a></strong> as usual.</li>
  </ul>
  
  <blockquote>
    <p><em>This interface to HTML5 document checking is deprecated. Use the Nu</em>
    <em>Html Checker at <a href="https://validator.w3.org/nu/" rel="nofollow">https://validator.w3.org/nu/</a> directly instead.</em></p>
  </blockquote>
  
  <p>So what is the meaning of this warning and why it shows up?</p>
  
  <p><strong>P.S</strong>. - I just noticed this is happening across my current projects and AFAIR since a few days ago.</p>
  
  <hr>
  
  <p><strong>EDIT</strong> - It stopped giving me the warning above, now it shows the following errors:</p>
  
  <blockquote>
    <p><strong><em>Error:</strong> Online parser error</em></p>
  </blockquote>
  
  <p>And</p>
  
  <blockquote>
    <p><strong><em>Error:</strong> Go to menu: HTML Validator/W3c Online validator to see the error</em></p>
  </blockquote>
  
  <p>Going to  <strong><a href="https://validator.w3.org" rel="nofollow">W3C Validator</a></strong> I can  now see it is updated for <strong><a href="https://validator.w3.org/nu/" rel="nofollow">W3C validator NU</a></strong></p>
  
  <p><strong>EDIT2</strong> - Since a while ago I've stopped seeing any error in the plugin. It looks the developers updated the plugin. So far so good.</p>