They don&#x27;t usually match on something as silly as the regexp &#x2F;ad&#x2F;, no—but they _do_ frequently contain a regexp like &#x2F;\bad\b&#x2F;.<p>The problem being—and this is painful personal experience speaking—web frameworks will frequently <i>also</i> cater to directory inode limits of caching reverse-proxies in their cache-busting code by doing something like this:<p><pre><code>    &quot;&#x2F;#{sha[0..1]}&#x2F;#{sha}.#{orig_ext}&quot;
</code></pre>
...which means that, for a SHA that <i>starts</i> with &quot;ad&quot;, you get an &quot;&#x2F;ad&#x2F;&quot; in the URL.