re class="typescript-code"><span class="tm-kw">class</span> <span class="tm-typ"><span class="className">C</span></span> { <span class="tm-vr">c</span>: <span class="tm-typ">any</span> }
<span class="tm-kw">function</span> <span class="tm-mth">f</span>(<span class="tm-vr">x</span>: <span class="tm-typ"><span class="className">C</span></span> | <span class="tm-typ">string</span>) {
  <span class="tm-kw">if</span> (<span class="tm-vr">x</span> <span class="tm-kw">instanceof</span> <span class="className">C</s