a data-link-type="dfn" href="https://drafts.csswg.org/selectors-4/#pseudo-class" id="ref-for-pseudo-class">pseudo-class</a>.</p>
   <p>Like built-in elements, <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/custom-elements.html#custom-element" id="ref-for-custom-element">custom elements</a> can have various states to be in too,
and <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/custom-elements.html#custom-element" id="ref-for-custom-element①">custom element</a> a