nk-type="dfn" href="https://infra.spec.whatwg.org/#ordered-set" id="ref-for-ordered-set①">set</a> of strings.</p>
   <p class="issue" id="issue-172e10b8"><a class="self-link" href="#issue-172e10b8"></a> Support customized built-in elements. <a href="https://github.com/whatwg/html/issues/5166">[whatwg/html Issue #5166]</a></p>
<pre class="idl highlight def"><c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="https://html.spec.whatwg.org/multipage/custom-elements.htm