 root node of the AST, which is used as the starting point.</p>
</li>
<li>
<p>An object containing callback functions for handling various kinds of nodes.</p>
</li>
<li>
<p>Another object that specifies what algorithm to use&mdash;we have set this to <code>null</code>
    to use the default because
    we don&rsquo;t particularly care about the order in which the nodes are processed.</p>
</li>
<li>
<p>Something we want passed in to each of the node handlers,
    which in our case is the <code>state</code> a