diff --git a/specification/v1_0/docs/a2ui_protocol.md b/specification/v1_0/docs/a2ui_protocol.md
index bbd1b93833..24817ebbb2 100644
--- a/specification/v1_0/docs/a2ui_protocol.md
+++ b/specification/v1_0/docs/a2ui_protocol.md
@@ -484,7 +484,7 @@ To ensure catalog schemas can be translated reliably into alternative, LLM-frien
    - All helper properties (such as common properties factored out of catalog items) MUST be inlined directly inside the properties block of each supporting component schema rather than referenced from a shared helper.
 3. **Restricted `$ref` Targets:**
    - Local `$ref` targets are restricted to referencing the catalog's top-level components or functions (e.g., `#/components/Text`, `#/functions/required`).
-   - External `$ref` targets MUST reference the standard types inside `common_types.json` (`https://a2ui.org/specification/v1_0/common_types.json#/$defs/...`), limited to the following allowed schemas:
+   - External `$ref` targets may reference other catalogs. When referencing `common_types.json` (`https://a2ui.org/specification/v1_0/common_types.json#/$defs/...`), targets are limited to the following allowed schemas:
      - `ComponentId`
      - `ChildList`
      - `DynamicString`
diff --git a/specification/v1_0/docs/evolution_guide.md b/specification/v1_0/docs/evolution_guide.md
index 5cf4b05a18..6ff7d18796 100644
--- a/specification/v1_0/docs/evolution_guide.md
+++ b/specification/v1_0/docs/evolution_guide.md
@@ -14,6 +14,7 @@ Version 1.0 differs from 0.9 in the following ways:
 - Standard JSON Schema metadata fields (`$schema`, `$id`, `title`, and `description`) are supported in catalogs, preventing validation failures on inline catalogs with strict property checks.
 - Identifier naming rules across all catalog entities (component names, function names, and argument keys) must conform to Unicode Standard Annex #31 (UAX #31).
 - The `@index` built-in function dynamically retrieves iteration indices during list template rendering. The `@` prefix is reserved for core system context evaluations.
+- Catalogs may now use `$ref` to reference other catalogs. This removes the requirement that catalogs be freestanding / have no external references except to core libraries.
 
 ## 2. Changes
 
@@ -25,6 +26,7 @@ Version 1.0 differs from 0.9 in the following ways:
 - Added an optional `instructions` field to the `Catalog` schema to embed design guidelines and component usage rules directly in the catalog, replacing the external `rules.txt` file.
 - Supported standard JSON Schema metadata fields (`$schema`, `$id`, `title`, and `description`) in the Catalog object definition. Since the Catalog schema restricts properties with `additionalProperties: false`, this ensures inline catalogs containing standard schema metadata do not fail schema validation.
 - Enforced Unicode Standard Annex #31 (UAX #31) identifier naming constraints (`XID_Start`, `XID_Continue`) across component names, function names, and argument keys.
+- Catalogs may now use `$ref` to reference other catalogs. This removes the requirement that catalogs be freestanding / have no external references except to core libraries.
 
 ### 2.2. Standard catalogs (basic)