anchor.diff:                </td>
                 <td>
                   <strong>array</strong> <span class="tag tag-success">Required</span>
  -                <p>A collection of elements.</p>
  -              </td>
  -            </tr>
  -            <tr>
  -              <td>
  -                <i>buttons</i>
  -              </td>
  -              <td>
  -                <strong>array</strong> <span class="tag tag-default">Optional</span>
  -                <p>A collection of objects.</p>
  +                <p>A collection of <code>element</code> objects.</p>
                 </td>
               </tr>
             </tbody>
  
positive.code:         "title": "Hello world!",
          "image_url": "http://example.com/example.png",
          "subtitle": "This is an example"
        }],
        "buttons": [{
          "type": "web_url",
          "url": "http://example.com",
          "title": "Show website"
        }]
      }
    }
  
negative.code: 
        <h2 class="page-header" id="types">Message types</h2>
  
        <p>Message types are broken down in four categories:</p>
  
        <div class="row">
          <div class="col-sm-6">
            <h5>Multimedia</h5>
            <ul>
              <li><code>image</code> </li>
              <li><code>audio</code> </li>
              <li><code>video</code> </li>
              <li><code>file</code> </li>
              <li><code>link</code></li>
              <li><code>sticker</code></li>
            </ul>
          </div>
          <div class="col-sm-6">
            <h5>Button</h5>
            <ul>
              <li><code>web_url</code> </li>
              <li><code>postback</code> </li>
              <li><code>call</code> </li>
              <li><code>share</code> </li>
              <li><code>buy</code></li>
            </ul>
          </div>
        </div>
  
        <div class="row">
          <div class="col-sm-6">
            <h5>Template</h5>
            <ul>
              <li><code>button</code> </li>
              <li><code>generic</code> </li>
              <li><code>list</code> </li>
              <li><code>receipt</code> </li>
            </ul>
          </div>
          <div class="col-sm-6">
            <h5>Other</h5>
            <ul>
              <li><code>location</code> </li>
            </ul>
          </div>
        </div>
  
        <hr class="my-3">
  
        <h3>Multimedia</h3>
  
        <p><code>mtype</code> must be one the following: <code>image</code>, <code>audio</code>, <code>video</code>, <code>file</code>, <code>link</code> or <code>sticker</code>.</p>
  
        <div class="card">
          <table class="table mb-0">
  