->]
<c- b>interface</c-> <a href="#customstateset"><code><c- g>CustomStateSet</c-></code></a> {
  <c- b>setlike</c->&lt;<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a>>;
  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-undefined"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-customstateset-add"><c- g>add</c-></a>(<a class="idl-code" data-link-type="interfac