title: What is the `&::` syntax in LESS CSS?
body: <p>I've been looking at twitter bootstrap and came across some syntax and I do not know what it does:</p>
  
  <p>From <a href="https://github.com/twitter/bootstrap/blob/master/less/buttons.less#L149" rel="noreferrer">buttons.less</a>:</p>
  
  <pre><code>button.btn,
  input[type="submit"].btn {
    &amp;::-moz-focus-inner {
    padding: 0;
      border: 0;
    }
  </code></pre>
  
  <p>What is the <code>&amp;::</code> in <code>&amp;::-moz-focus-inner</code> for?</p>
  
  <p>I know the <code>&amp;</code> is for a 'parent selector' and that a <code>:</code> is part of the syntax for a pseudo selector such as <code>:hover</code>, but what is the second <code>:</code> for?</p>
  
  <p><em>Ps.</em> I've also been looking for a LESS syntax reference but I cannot find any documentation about LESS other than the one page at lesscss.org. Is there no documenation for LESS other than that one page?</p>