hod" data-export data-lt="add(value)|add" id="dom-customstateset-add"><code>add(<var>value</var>)</code></dfn>
method, when invoked, must run these steps:</p>
   <ol>
    <li>
     <p>If <var>value</var> does not match to <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-4/#typedef-dashed-ident" id="ref-for-typedef-dashed-ident">&lt;dashed-ident></a>, then
 <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#dfn-throw" id="ref-for-dfn-throw">throw</a> a "<co