1.html

<!DOCTYPE html>
<link rel="stylesheet" href="styles.css" />
<link rel="stylesheet"
      href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css">
<style>
layout { display: layout(sizing); }
</style>
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/highlight.min.js"></script>
<div id="controls">
  <label>A - max-height <input type="number" data-unit="px" value="20" step="10" />px</label>
</div>

<pre><code class="js">
registerLayout('sizing', class {
  *intrinsicSizes() { /* not yet implemented */ }

  *layout() {
    return {autoBlockSize: 100};
  }
});
</code></pre>

<pre><code class="html"></code></pre>

<div id="wrapper">
<layout id="A"></layout>
</div>

<script src="script.js"></script>