microsoft · janechu · Jun 4, 2026
@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Add a registry path export for FAST element definition lookups.",
+  "packageName": "@microsoft/fast-element",
+  "email": "7559015+janechu@users.noreply.github.com",
+  "dependentChangeType": "none"
+}
@@ -53,7 +53,9 @@ For deep dives into specific areas, see the linked detailed documents.
 The library's kernel is module-scoped rather than stored on `globalThis`: import `FAST` from `@microsoft/fast-element`, `Updates` from `@microsoft/fast-element`, and `Observable` from `@microsoft/fast-element`.
 
 The root entrypoint exports the FAST Element implementation APIs. Focused package
-path exports remain available when a consumer wants a narrower entrypoint.
+path exports remain available when a consumer wants a narrower entrypoint,
+including `@microsoft/fast-element/registry.js` for FAST element definition
+lookups.
 
 ---
 
@@ -99,7 +101,7 @@ The previous `FAST.getById()` slot registry, `FASTGlobal` type, and `KernelServi
 - `onAttributeChangedCallback()` is the standard handler that processes attribute changes. During the prerendered bind, it is temporarily swapped to a no-op (see above) to avoid redundant processing of server-rendered attribute values.
 - Exposes `addBehavior` / `removeBehavior` for dynamic `HostBehavior` management (used by `ElementStyles`).
 
-`FASTElementDefinition` wraps all the metadata for a custom element class: its tag name, template, styles, and observed attribute list. It is created by `FASTElement.compose()` (which returns `Promise<FASTElementDefinition>`, always resolving immediately) and registered globally via `fastElementRegistry`. `PartialFASTElementDefinition.template` may be either a concrete `ElementViewTemplate<InstanceType<TType>>` or a `FASTElementTemplateResolver<TType>` function that receives the composed definition and returns the concrete template (sync or async). `FASTElementDefinition.template` always stores the concrete `ElementViewTemplate<InstanceType<TType>>` after composition or resolver settlement. `FASTElement.define()` returns `Promise<TType>` — resolving immediately for complete definitions or definitions without an initial template, and resolving async template resolver functions only after extensions have had a chance to update the definition. `FASTElementDefinition.register()` returns `Promise<Function>` — resolving when a definition with the given name has been registered.
+`FASTElementDefinition` wraps all the metadata for a custom element class: its tag name, template, styles, and observed attribute list. It is created by `FASTElement.compose()` (which returns `Promise<FASTElementDefinition>`, always resolving immediately) and registered globally via `fastElementRegistry`. Consumers that need focused access to definition lookup can import `fastElementRegistry` from `@microsoft/fast-element/registry.js`. `PartialFASTElementDefinition.template` may be either a concrete `ElementViewTemplate<InstanceType<TType>>` or a `FASTElementTemplateResolver<TType>` function that receives the composed definition and returns the concrete template (sync or async). `FASTElementDefinition.template` always stores the concrete `ElementViewTemplate<InstanceType<TType>>` after composition or resolver settlement. `FASTElement.define()` returns `Promise<TType>` — resolving immediately for complete definitions or definitions without an initial template, and resolving async template resolver functions only after extensions have had a chance to update the definition. `FASTElementDefinition.register()` returns `Promise<Function>` — resolving when a definition with the given name has been registered.
 
 #### Extensions
 
@@ -535,6 +537,7 @@ src/
 ├── metadata.ts            # Reflect-based metadata helpers
 ├── utilities.ts           # UnobservableMutationObserver and other helpers
 ├── debug.ts               # Exports enableDebug() for human-readable FAST errors
+├── registry.ts            # fastElementRegistry focused path export
 ├── observation/
 │   ├── observable.ts      # Observable, @observable, ExpressionNotifier, ExecutionContext
 │   ├── notifier.ts        # Subscriber, Notifier, SubscriberSet, PropertyChangeNotifier

@@ -81,8 +81,10 @@ Bundle sizes for each tree-shakeable export are tracked in [`SIZES.md`](./SIZES.
 The root `@microsoft/fast-element` entrypoint exports the FAST Element
 implementation APIs, including the element base class, kernel, controller,
 definition APIs, template APIs, binding helpers, directives, styles, and schema
-helpers. Declarative, hydration, context, and dependency injection APIs are
-available from their focused path exports.
+helpers. The FAST element registry is also available from
+`@microsoft/fast-element/registry.js` for focused definition lookups.
+Declarative, hydration, context, and dependency injection APIs are available
+from their focused path exports.
 
 Focused package path exports remain available for consumers that want to import
 a narrower entrypoint directly. The website's

@@ -571,9 +571,7 @@ export class FASTElementDefinition<TType extends Constructable<HTMLElement> = Co
 // @public
 export type FASTElementExtension = (definition: FASTElementDefinition) => void;
 
-// Warning: (ae-internal-missing-underscore) The name "fastElementRegistry" should be prefixed with an underscore because the declaration is marked as @internal
-//
-// @internal
+// @public
 export const fastElementRegistry: TypeRegistry<FASTElementDefinition>;
 
 // @public
@@ -1177,16 +1175,15 @@ export const TwoWaySettings: Readonly<{
     configure(settings: TwoWaySettings): void;
 }>;
 
-// Warning: (ae-forgotten-export) The symbol "TypeDefinition" needs to be exported by the entry point index.d.ts
-// Warning: (ae-internal-missing-underscore) The name "TypeRegistry" should be prefixed with an underscore because the declaration is marked as @internal
-//
-// @internal
+// @public
+export interface TypeDefinition {
+    type: Function;
+}
+
+// @public
 export interface TypeRegistry<TDefinition extends TypeDefinition> {
-    // (undocumented)
     getByType(key: Function): TDefinition | undefined;
-    // (undocumented)
     getForInstance(object: any): TDefinition | undefined;
-    // (undocumented)
     register(definition: TDefinition): boolean;
 }
 

@@ -118,7 +118,9 @@ The DOM after hydration should look like this:
 
 ### Fast Element Registry
 
-The `fastElementRegistry` serves as the central coordination point between the two packages:
+The `fastElementRegistry` serves as the central coordination point between the
+two packages and is available to consumers from
+`@microsoft/fast-element/registry.js`:
 
 - Stores partial element definitions created by `define()`
 - Provides lookup mechanism via `register()` for template attachment

@@ -35,6 +35,11 @@
       "test": "./src/components/fast-element.ts",
       "default": "./dist/esm/components/fast-element.js"
     },
+    "./registry.js": {
+      "types": "./dist/dts/registry.d.ts",
+      "test": "./src/registry.ts",
+      "default": "./dist/esm/registry.js"
+    },
     "./declarative.js": {
       "types": "./dist/dts/declarative/index.d.ts",
       "test": "./src/declarative/index.ts",

@@ -1,6 +1,10 @@
 import { type Constructable, isFunction, isString } from "../interfaces.js";
 import { Observable } from "../observation/observable.js";
-import { createTypeRegistry, type TypeRegistry } from "../platform.js";
+import {
+    createTypeRegistry,
+    type TypeDefinition,
+    type TypeRegistry,
+} from "../platform.js";
 import { type ComposableStyles, ElementStyles } from "../styles/element-styles.js";
 import type { ElementViewTemplate } from "../templating/template.js";
 import { type AttributeConfiguration, AttributeDefinition } from "./attributes.js";
@@ -11,13 +15,16 @@ const defaultElementOptions: ElementDefinitionOptions = {};
 const fastElementBaseTypes = new Set<Function>();
 
 /**
- * The FAST custom element registry
- * @internal
+ * The FAST custom element registry.
+ * @remarks
+ * This registry stores FAST element definitions by constructor so consumers can
+ * look up the `FASTElementDefinition` associated with an element type or instance.
+ * @public
  */
 export const fastElementRegistry: TypeRegistry<FASTElementDefinition> =
     createTypeRegistry<FASTElementDefinition>();
 
-export type { TypeRegistry };
+export type { TypeDefinition, TypeRegistry };
 
 /**
  * Shadow root initialization options.

@@ -30,6 +30,41 @@ test.describe("extension subpaths", () => {
         expect(result.hasSchema).toBe(true);
     });
 
+    test("exports the FAST element registry from the registry subpath", async ({
+        page,
+    }) => {
+        await page.goto("/");
+
+        const result = await page.evaluate(async () => {
+            // @ts-expect-error: Client module.
+            const { FASTElementDefinition, fastElementRegistry } = await import(
+                "/extension-subpaths-main.js"
+            );
+
+            class RegistrySubpathElement extends HTMLElement {}
+
+            const name = `registry-subpath-element-${crypto.randomUUID()}`;
+            const definition = await FASTElementDefinition.compose(
+                RegistrySubpathElement,
+                { name },
+            );
+            definition.define();
+            const instance = document.createElement(name);
+
+            return {
+                hasRegistry: typeof fastElementRegistry.getByType === "function",
+                getByTypeReturnsDefinition:
+                    fastElementRegistry.getByType(RegistrySubpathElement) === definition,
+                getForInstanceReturnsDefinition:
+                    fastElementRegistry.getForInstance(instance) === definition,
+            };
+        });
+
+        expect(result.hasRegistry).toBe(true);
+        expect(result.getByTypeReturnsDefinition).toBe(true);
+        expect(result.getForInstanceReturnsDefinition).toBe(true);
+    });
+
     test("observerMap accepts a schema for non-declarative use", async ({ page }) => {
         await page.goto("/");
 

@@ -33,6 +33,7 @@ export type {
     FASTElementTemplateResolver,
     PartialFASTElementDefinition,
     ShadowRootOptions,
+    TypeDefinition,
     TypeRegistry,
 } from "./components/fast-definitions.js";
 export {

@@ -50,20 +50,38 @@ export function getDebugMessageLookup(): Record<number, string> {
 export const emptyArray = Object.freeze([]);
 
 /**
- * Do not change. Part of shared kernel contract.
- * @internal
+ * A type that can be registered with a `TypeRegistry`.
+ * @public
  */
 export interface TypeDefinition {
+    /**
+     * The registered type constructor.
+     */
     type: Function;
 }
 
 /**
- * Do not change. Part of shared kernel contract.
- * @internal
+ * A registry that stores definitions by type.
+ * @public
  */
 export interface TypeRegistry<TDefinition extends TypeDefinition> {
+    /**
+     * Registers a type definition.
+     * @param definition - The type definition to register.
+     * @returns `true` when the definition was registered, otherwise `false`.
+     */
     register(definition: TDefinition): boolean;
+
+    /**
+     * Gets a definition by type.
+     * @param key - The type to retrieve the definition for.
+     */
     getByType(key: Function): TDefinition | undefined;
+
+    /**
+     * Gets a definition by instance.
+     * @param object - The instance to retrieve the definition for.
+     */
     getForInstance(object: any): TDefinition | undefined;
 }
 

@@ -0,0 +1,6 @@
+export {
+    FASTElementDefinition,
+    fastElementRegistry,
+    type TypeDefinition,
+    type TypeRegistry,
+} from "./components/fast-definitions.js";
@@ -6,4 +6,8 @@ export {
     ObserverMap,
     observerMap,
 } from "@microsoft/fast-element/observer-map.js";
+export {
+    FASTElementDefinition,
+    fastElementRegistry,
+} from "@microsoft/fast-element/registry.js";
 export { Schema } from "../src/components/schema.js";
@@ -26,6 +26,7 @@ This table is generated from the `exports` field in `@microsoft/fast-element/pac
 | `@microsoft/fast-element` | Root implementation export for FAST Element APIs. | `./dist/esm/index.js` | `./dist/dts/index.d.ts` |
 | `@microsoft/fast-element/debug.js` | Debug message helpers. | `./dist/esm/debug.js` | `./dist/dts/debug.d.ts` |
 | `@microsoft/fast-element/fast-element.js` | FASTElement and the customElement decorator. | `./dist/esm/components/fast-element.js` | `./dist/dts/components/fast-element.d.ts` |
+| `@microsoft/fast-element/registry.js` | FAST element definition registry APIs. | `./dist/esm/registry.js` | `./dist/dts/registry.d.ts` |
 | `@microsoft/fast-element/declarative.js` | Path-only declarative template APIs. | `./dist/esm/declarative/index.js` | `./dist/dts/declarative/index.d.ts` |
 | `@microsoft/fast-element/declarative-utilities.js` | Declarative parser and observer-map utilities. | `./dist/esm/declarative/utilities.js` | `./dist/dts/declarative/utilities.d.ts` |
 | `@microsoft/fast-element/attribute-map.js` | Schema-driven attribute map extension. | `./dist/esm/declarative/attribute-map.js` | `./dist/dts/declarative/attribute-map.d.ts` |

@@ -0,0 +1,28 @@
+---
+id: "fast-element.fastelementregistry"
+title: "fastElementRegistry variable"
+layout: 3x-api
+eleventyNavigation:
+  key: "api3xfast-element.fastelementregistry"
+  parent: "api3xfast-element"
+  title: "fastElementRegistry variable"
+navigationOptions:
+  activeKey: "api3xfast-element.fastelementregistry"
+---
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[@microsoft/fast-element](../fast-element/index.html) &gt; [fastElementRegistry](../fast-element.fastelementregistry/index.html)
+
+## fastElementRegistry variable
+
+The FAST custom element registry.
+
+**Signature:**
+
+```typescript
+fastElementRegistry: TypeRegistry<FASTElementDefinition>
+```
+
+## Remarks
+
+This registry stores FAST element definitions by constructor so consumers can look up the `FASTElementDefinition` associated with an element type or instance.
@@ -1284,6 +1284,28 @@ Lifecycle callbacks for template events.
 The settings required to enable two-way binding.
 
 
+</td></tr>
+<tr><td>
+
+[TypeDefinition](../fast-element.typedefinition/)
+
+
+</td><td>
+
+A type that can be registered with a `TypeRegistry`<!-- -->.
+
+
+</td></tr>
+<tr><td>
+
+[TypeRegistry](../fast-element.typeregistry/)
+
+
+</td><td>
+
+A registry that stores definitions by type.
+
+
 </td></tr>
 <tr><td>
 
@@ -1519,6 +1541,17 @@ The FAST messaging API for warnings and errors.
 A minimal base class for FASTElements that also provides static helpers for working with FASTElements.
 
 
+</td></tr>
+<tr><td>
+
+[fastElementRegistry](../fast-element.fastelementregistry/)
+
+
+</td><td>
+
+The FAST custom element registry.
+
+
 </td></tr>
 <tr><td>
 

@@ -0,0 +1,68 @@
+---
+id: "fast-element.typedefinition"
+title: "TypeDefinition interface"
+layout: 3x-api
+eleventyNavigation:
+  key: "api3xfast-element.typedefinition"
+  parent: "api3xfast-element"
+  title: "TypeDefinition interface"
+navigationOptions:
+  activeKey: "api3xfast-element.typedefinition"
+---
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[@microsoft/fast-element](../fast-element/index.html) &gt; [TypeDefinition](../fast-element.typedefinition/index.html)
+
+## TypeDefinition interface
+
+A type that can be registered with a `TypeRegistry`<!-- -->.
+
+**Signature:**
+
+```typescript
+export interface TypeDefinition
+```
+
+## Properties
+
+<table><thead><tr><th>
+
+Property
+
+
+</th><th>
+
+Modifiers
+
+
+</th><th>
+
+Type
+
+
+</th><th>
+
+Description
+
+
+</th></tr></thead>
+<tbody><tr><td>
+
+[type](../fast-element.typedefinition.type/)
+
+
+</td><td>
+
+
+</td><td>
+
+Function
+
+
+</td><td>
+
+The registered type constructor.
+
+
+</td></tr>
+</tbody></table>