title: All list of values for HTML rel attribute
body: <p>I would like to know more on <code>rel</code> attribute used with <code>a</code> html elements.
  Does anyone know some list of attributes useful for SEO and social?</p>
  
  <pre><code>&lt;a title="" rel="friend met neighbor" href="#"&gt;This is a link&lt;/a&gt;
  </code></pre>
  
  <p>I know it only inside <code>WordPress</code> and it's links manager, but nothing more.</p>