provide the mapping from <code>number</code> to
<code>Number</code>. Whenever the compiler needs to get properties of some type,
it asks for the apparent type of that type first.
The other types that have interesting apparent types are type parameters:</p>
<p><pre class="typescript-code"><span class="tm-kw">interface</span> <span class="tm-typ"><span class="interfaceName">Node</span></span> {
  <span class="tm-vr">parent</span>: <span class="tm-typ"><span class="interfaceName">Node</span></span>;
  <span cl