Why can't you create Custom Elements in Chrome Extensions? : <p>I attempted to create a custom element in a Chrome extension but <code>customeElements.define</code> is <code>null</code>.</p>

<pre><code>customElements.define('customElement', class extends HTMLElement {
    constructor() {
        super();
    }
    ...
});
</code></pre>

<p>So apparently Chrome doesn't want extensions to create custom elements. But why? Is it a security risk? </p>

<p>I can't seem to find anything in Chrome's extension guide that says it's not allowed.</p>
