 of compare.  Sorts an array of versions
in descending order when passed to <code>Array.sort()</code>.</li>
<li><code>diff(v1, v2)</code>: Returns difference between two versions by the release type
(<code>major</code>, <code>premajor</code>, <code>minor</code>, <code>preminor</code>, <code>patch</code>, <code>prepatch</code>, or <code>prerelease</code>),
or null if the versions are the same.</li>
</ul>
<h3 id="ranges">Ranges</h3>
<ul>
<li><code>validRange(range)</code>: Return the valid range or null if it