A first version that has some working standard features.

tp-rtb-undo.js

@@ -0,0 +1,23 @@
+import { html } from 'lit';
+import { TpRtbBaseExtension } from './tp-rtb-base-extension.js';
+
+class TpRtbUndo extends TpRtbBaseExtension {
+  constructor() {
+    super();
+    this.label = 'Undo';
+  }
+
+  render() {
+    return html`
+      ${super.render()}
+    `;
+  }
+
+  _handleClick() {
+    if (this.parentEditor) {
+      this.parentEditor.undo();
+    }
+  }
+}
+
+customElements.define('tp-rtb-undo', TpRtbUndo);