diff --git a/packages/idb-bridge/src/util/structuredClone.ts b/packages/idb-bridge/src/util/structuredClone.ts
index 5ed269db3..a3842b8c4 100644
--- a/packages/idb-bridge/src/util/structuredClone.ts
+++ b/packages/idb-bridge/src/util/structuredClone.ts
@@ -14,6 +14,29 @@
  permissions and limitations under the License.
 */
 
+/**
+ * Encoding (new, compositional version):
+ * 
+ * Encapsulate object that itself might contain a "$" field:
+ * { $: { E... } }
+ * Circular reference:
+ * { $: ["ref", uplevel, field...] }
+ * Date:
+ * { $: ["data"], val: datestr }
+ * Bigint:
+ * { $: ["bigint"], val: bigintstr }
+ * Array with special (non-number) attributes:
+ * { $: ["array"], val: arrayobj }
+ * Undefined field
+ * { $: "undef" }
+ * 
+ * Legacy (top-level only), for backwards compatibility:
+ * { $types: [...] }
+ */
+
+/**
+ * Imports.
+ */
 import { DataCloneError } from "./errors.js";
 
 const { toString: toStr } = {};
@@ -73,10 +96,6 @@ function isUserObject(val: any): boolean {
   return hasConstructorOf(val, Object) || isUserObject(proto);
 }
 
-function isRegExp(val: any): boolean {
-  return toStringTag(val) === "RegExp";
-}
-
 function copyBuffer(cur: any) {
   if (cur instanceof Buffer) {
     return Buffer.from(cur);
@@ -334,8 +353,7 @@ export function structuredEncapsulate(val: any): any {
   return res;
 }
 
-export function internalStructuredRevive(val: any): any {
-  val = JSON.parse(JSON.stringify(val));
+export function applyLegacyTypeAnnotations(val: any): any {
   if (val === null) {
     return null;
   }
@@ -417,8 +435,14 @@ export function internalStructuredRevive(val: any): any {
   return outRoot;
 }
 
+export function internalStructuredRevive(val: any): any {
+  // FIXME: Do the newly specified, compositional encoding here.
+  val = JSON.parse(JSON.stringify(val));
+}
+
 export function structuredRevive(val: any): any {
-  return internalStructuredRevive(val);
+  const r = internalStructuredRevive(val);
+  return applyLegacyTypeAnnotations(r);
 }
 
 /**