Dynamic tags for lit-html not possible?

Can anyone tell me why I cannot use variables within lit-html's html method?

const h1 = 'h1';
return html`
  <${h1} class="a-heading ${classes}">
    <slot></slot>
  </${h1}>
`;

If I replace ${h1} with h1 that works without problems.

For everyone interested in my solution: Use unsafeHTML if you can (you should not do that if you wrap any input fields within).

    import { unsafeHTML } from 'lit-html/directives/unsafe-html';
   
     // ...

    const template = `
      <h${this.rank} class="a-heading">
        <slot></slot>
      </h${this.rank}>
    `;

    return html`
      ${unsafeHTML(template)}
    `;