mg src="./walk-tree.svg" alt="Walking a tree"/>
  <figcaption markdown="1">Figure 14.2: Walking a tree to perform an operation at each node.</figcaption>
</figure>

<h2 id="style-checker-apply">Section 14.4: How can we apply checks?</h2>
<p>We don&rsquo;t just want to collect nodes:
we want to check their properties against a set of rules.
One way to do this would be to call <code>walk.simple</code> once for each rule,
passing it a function that checks just that rule.
Another way&mdash;the one we&rsquo;ll u