"content">Motivation</span><a class="self-link" href="#motivation"></a></h3>
   <p>Build-in elements provided by user agents have certain “states” that can change
over time depending on user interaction and other factors, and are exposed to
web authors through pseudo classes. For example, some form controls have the
“invalid” state, which is exposed through the <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/selectors-4/#invalid-pseudo" id="ref-for-invalid-pseudo">:invalid</a> <