diff --git a/specification/v1_0/catalogs/basic/catalog.json b/specification/v1_0/catalogs/basic/catalog.json
index ad070a4e8..d0fd59744 100644
--- a/specification/v1_0/catalogs/basic/catalog.json
+++ b/specification/v1_0/catalogs/basic/catalog.json
@@ -12,9 +12,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -30,6 +27,10 @@
               "description": "A hint for the base text style.",
               "enum": ["caption", "body"],
               "default": "body"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "text"]
@@ -43,9 +44,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -71,6 +69,10 @@
               "description": "A hint for the image size and style.",
               "enum": ["icon", "avatar", "smallFeature", "mediumFeature", "largeFeature", "header"],
               "default": "mediumFeature"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "url"]
@@ -84,9 +86,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -171,6 +170,10 @@
                   "additionalProperties": false
                 }
               ]
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "name"]
@@ -184,9 +187,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -200,6 +200,10 @@
             "posterUrl": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicString",
               "description": "The URL of the poster image to display before the video plays."
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "url"]
@@ -213,9 +217,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -229,6 +230,10 @@
             "description": {
               "description": "A description of the audio, such as a title or summary.",
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicString"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "url"]
@@ -242,9 +247,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "description": "A layout component that arranges its children horizontally. To create a grid layout, nest Columns within this Row.",
@@ -275,6 +277,10 @@
               "description": "Defines the alignment of children along the cross axis (vertically). This is similar to the CSS 'align-items' property, but uses camelCase values (e.g., 'start').",
               "enum": ["start", "center", "end", "stretch"],
               "default": "stretch"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "children"]
@@ -288,9 +294,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "description": "A layout component that arranges its children vertically. To create a grid layout, nest Rows within this Column.",
@@ -321,6 +324,10 @@
               "description": "Defines the alignment of children along the cross axis (horizontally). This is similar to the CSS 'align-items' property.",
               "enum": ["center", "end", "start", "stretch"],
               "default": "stretch"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "children"]
@@ -334,9 +341,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -358,6 +362,10 @@
               "description": "Defines the alignment of children along the cross axis.",
               "enum": ["start", "center", "end", "stretch"],
               "default": "stretch"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "children"]
@@ -371,9 +379,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -383,6 +388,10 @@
             "child": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentId",
               "description": "The ID of the single child component to be rendered inside the card. To display multiple elements, you MUST wrap them in a layout component (like Column or Row) and pass that container's ID here. Do NOT pass multiple IDs or a non-existent ID. Do NOT define the child component inline."
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "child"]
@@ -396,9 +405,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -424,6 +430,10 @@
                 "required": ["title", "child"],
                 "additionalProperties": false
               }
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "tabs"]
@@ -437,9 +447,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -453,6 +460,10 @@
             "content": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentId",
               "description": "The ID of the component to be displayed inside the modal. Do NOT define the component inline."
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "trigger", "content"]
@@ -466,9 +477,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "type": "object",
           "properties": {
@@ -480,6 +488,10 @@
               "description": "The orientation of the divider.",
               "enum": ["horizontal", "vertical"],
               "default": "horizontal"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component"]
@@ -493,9 +505,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
         },
@@ -517,6 +526,10 @@
             },
             "action": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Action"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "child", "action"]
@@ -530,9 +543,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
         },
@@ -559,6 +569,10 @@
               "description": "The type of input field to display.",
               "enum": ["longText", "number", "shortText", "obscured"],
               "default": "shortText"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "label"]
@@ -572,9 +586,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
         },
@@ -591,6 +602,10 @@
             "value": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicBoolean",
               "description": "The current state of the checkbox (true for checked, false for unchecked)."
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "label", "value"]
@@ -604,9 +619,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
         },
@@ -660,6 +672,10 @@
               "type": "boolean",
               "description": "If true, displays a search input to filter the options.",
               "default": false
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "options", "value"]
@@ -673,9 +689,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
         },
@@ -706,6 +719,10 @@
               "type": "integer",
               "minimum": 1,
               "description": "The number of discrete divisions in the slider range. If specified, the slider will snap to discrete values."
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "value", "max"]
@@ -719,9 +736,6 @@
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
         },
-        {
-          "$ref": "#/$defs/CatalogComponentCommon"
-        },
         {
           "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
         },
@@ -800,6 +814,10 @@
             "label": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicString",
               "description": "The text label for the input field."
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "value"]
@@ -1222,15 +1240,6 @@
     }
   },
   "$defs": {
-    "CatalogComponentCommon": {
-      "type": "object",
-      "properties": {
-        "weight": {
-          "type": "number",
-          "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
-        }
-      }
-    },
     "surfaceProperties": {
       "type": "object",
       "properties": {
diff --git a/specification/v1_0/catalogs/minimal/catalog.json b/specification/v1_0/catalogs/minimal/catalog.json
index 7b1bc39bf..42b29fac3 100644
--- a/specification/v1_0/catalogs/minimal/catalog.json
+++ b/specification/v1_0/catalogs/minimal/catalog.json
@@ -8,18 +8,25 @@
     "Text": {
       "type": "object",
       "allOf": [
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"},
-        {"$ref": "#/$defs/CatalogComponentCommon"},
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
+        },
         {
           "type": "object",
           "properties": {
-            "component": {"const": "Text"},
+            "component": {
+              "const": "Text"
+            },
             "text": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicString"
             },
             "variant": {
               "type": "string",
               "enum": ["caption", "body"]
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "text"]
@@ -30,12 +37,15 @@
     "Row": {
       "type": "object",
       "allOf": [
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"},
-        {"$ref": "#/$defs/CatalogComponentCommon"},
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
+        },
         {
           "type": "object",
           "properties": {
-            "component": {"const": "Row"},
+            "component": {
+              "const": "Row"
+            },
             "children": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ChildList"
             },
@@ -54,6 +64,10 @@
             "align": {
               "type": "string",
               "enum": ["start", "center", "end", "stretch"]
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "children"]
@@ -64,12 +78,15 @@
     "Column": {
       "type": "object",
       "allOf": [
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"},
-        {"$ref": "#/$defs/CatalogComponentCommon"},
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
+        },
         {
           "type": "object",
           "properties": {
-            "component": {"const": "Column"},
+            "component": {
+              "const": "Column"
+            },
             "children": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ChildList"
             },
@@ -88,6 +105,10 @@
             "align": {
               "type": "string",
               "enum": ["center", "end", "start", "stretch"]
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "children"]
@@ -98,13 +119,18 @@
     "Button": {
       "type": "object",
       "allOf": [
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"},
-        {"$ref": "#/$defs/CatalogComponentCommon"},
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"},
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
+        },
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
+        },
         {
           "type": "object",
           "properties": {
-            "component": {"const": "Button"},
+            "component": {
+              "const": "Button"
+            },
             "child": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentId"
             },
@@ -114,6 +140,10 @@
             },
             "action": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Action"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
             }
           },
           "required": ["component", "child", "action"]
@@ -124,13 +154,18 @@
     "TextField": {
       "type": "object",
       "allOf": [
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"},
-        {"$ref": "#/$defs/CatalogComponentCommon"},
-        {"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"},
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"
+        },
+        {
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/Checkable"
+        },
         {
           "type": "object",
           "properties": {
-            "component": {"const": "TextField"},
+            "component": {
+              "const": "TextField"
+            },
             "label": {
               "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicString"
             },
@@ -141,7 +176,13 @@
               "type": "string",
               "enum": ["longText", "number", "shortText", "obscured"]
             },
-            "validationRegexp": {"type": "string"}
+            "validationRegexp": {
+              "type": "string"
+            },
+            "weight": {
+              "type": "number",
+              "description": "The relative weight of this component within a Row or Column. This is similar to the CSS 'flex-grow' property. Note: this may ONLY be set when the component is a direct descendant of a Row or Column."
+            }
           },
           "required": ["component", "label"]
         }
@@ -155,7 +196,9 @@
       "description": "Converts an input string to a capitalized version.",
       "returnType": "string",
       "properties": {
-        "call": {"const": "capitalize"},
+        "call": {
+          "const": "capitalize"
+        },
         "args": {
           "type": "object",
           "properties": {
@@ -172,12 +215,6 @@
     }
   },
   "$defs": {
-    "CatalogComponentCommon": {
-      "type": "object",
-      "properties": {
-        "weight": {"type": "number"}
-      }
-    },
     "surfaceProperties": {
       "type": "object",
       "properties": {},
@@ -185,16 +222,32 @@
     },
     "anyComponent": {
       "oneOf": [
-        {"$ref": "#/components/Text"},
-        {"$ref": "#/components/Row"},
-        {"$ref": "#/components/Column"},
-        {"$ref": "#/components/Button"},
-        {"$ref": "#/components/TextField"}
+        {
+          "$ref": "#/components/Text"
+        },
+        {
+          "$ref": "#/components/Row"
+        },
+        {
+          "$ref": "#/components/Column"
+        },
+        {
+          "$ref": "#/components/Button"
+        },
+        {
+          "$ref": "#/components/TextField"
+        }
       ],
-      "discriminator": {"propertyName": "component"}
+      "discriminator": {
+        "propertyName": "component"
+      }
     },
     "anyFunction": {
-      "oneOf": [{"$ref": "#/functions/capitalize"}]
+      "oneOf": [
+        {
+          "$ref": "#/functions/capitalize"
+        }
+      ]
     }
   }
 }
diff --git a/specification/v1_0/docs/a2ui_protocol.md b/specification/v1_0/docs/a2ui_protocol.md
index 265db473f..221297fce 100644
--- a/specification/v1_0/docs/a2ui_protocol.md
+++ b/specification/v1_0/docs/a2ui_protocol.md
@@ -473,6 +473,177 @@ To ensure complete cross-language compatibility across client SDKs, parsers, and
   - `1stItem` (violates initial `Nd`)
   - `submit-form`, `user#name`, `calc$val` (violates `Pattern_Syntax`)
 
+#### Catalog Schema Rules and Conventions
+
+To ensure catalog schemas can be translated reliably into alternative, LLM-friendly DSL formats (e.g., HTML-like XML, functional, or compact inline formats), cleanly mapped to type-safe client SDK representations, automatically parsed, and bound seamlessly across platforms, all v1.0 component and function catalog definitions MUST conform to the following strict structural constraints and conventions:
+
+1. **Strict Top-Level vs. `$defs` Boundary:**
+   - **Top-Level components and functions:** All component and function schemas MUST be declared directly under the top-level keys `"components"` and `"functions"` respectively.
+   - **External References inside `$defs`:** Any definition referenced externally (e.g., from the envelope schema `server_to_client.json` or `common_types.json`) MUST reside inside the `"$defs"` object at the catalog root. This strictly includes:
+     - `surfaceProperties`: Referenced as `catalog.json#/$defs/surfaceProperties`.
+     - `anyComponent`: Referenced as `catalog.json#/$defs/anyComponent`.
+     - `anyFunction`: Referenced as `catalog.json#/$defs/anyFunction`.
+2. **No Custom `$defs` or Helpers:**
+   - To prevent unconstrained branching, custom definitions or shared helper schemas inside a catalog are strictly prohibited under `"$defs"`.
+   - The only allowed keys within the catalog's `"$defs"` object are `anyComponent`, `anyFunction`, and `surfaceProperties`.
+   - All helper properties (such as common properties factored out of catalog items) MUST be inlined directly inside the properties block of each supporting component schema rather than referenced from a shared helper.
+3. **Restricted `$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#/$defs/...`), limited to the following allowed schemas:
+     - `ComponentId`
+     - `ChildList`
+     - `DynamicString`
+     - `DynamicNumber`
+     - `DynamicBoolean`
+     - `DynamicStringList`
+     - `DynamicValue`
+     - `CheckRule`
+     - `ComponentCommon`
+     - `Checkable`
+     - `Action`
+4. **Component Discriminator Rule:**
+   - Every component schema defined inside the `components` map must have a required property named `component` whose value is a constant (`const`) matching the key under which it is defined.
+   - Example: The component defined at `components.Text` must declare:
+     ```json
+     "properties": {
+       "component": {
+         "const": "Text"
+       }
+     }
+     ```
+     This enables route-dispatch matching via the `discriminator` block inside `anyComponent` (designating `"propertyName": "component"`).
+5. **Standard Component Structure:**
+   - All components defined in the `components` object must use an `allOf` structure that combines:
+     1. An external reference to the baseline identity and accessibility attributes:
+        `{"$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon"}`
+     2. A local object schema defining the unique properties of that specific component (e.g., its children, variant, specific layouts).
+6. **Strict Function Interface Pattern:**
+   - Every function schema defined inside the `functions` map must validate a wire-level `FunctionCall` object. This requires:
+     - A `properties` block with a `call` property containing a constant of the function's name (e.g., `"call": { "const": "email" }`).
+     - An optional `args` property representing arguments (or absent if the function accepts no arguments).
+     - Mandatory metadata fields outside the strict JSON validation properties to advertise interface details:
+       - **`returnType`**: Must be a string enum indicating the return type (`string`, `number`, `boolean`, `array`, `object`, `any`, or `void`).
+       - **`callableFrom`**: Must be a string enum indicating the execution boundary (`clientOnly`, `remoteOnly`, or `clientOrRemote`). If omitted, it defaults to `clientOnly`.
+7. **Strict Top-Level Schema Keys:**
+   - To keep catalog schemas predictable and prevent custom extensions from polluting the global file space, a `catalog.json` file is restricted to the following root-level keys:
+     - `$schema`
+     - `$id`
+     - `title`
+     - `description`
+     - `catalogId`
+     - `instructions`
+     - `components`
+     - `functions`
+     - `$defs`
+   - No other top-level keys are permitted.
+
+##### Example Schema Template
+
+Below is an annotated, fully compliant `catalog.json` schema template (written in JSONC format with comments) representing a visual, complete model of these rules in action:
+
+```jsonc
+{
+  // Rule 7: Strict Top-Level Schema Keys
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://a2ui.org/specification/v1_0/catalogs/basic/catalog.json",
+  "title": "A2UI Basic Catalog Template",
+  "description": "An annotated example showcasing structural rules and conventions.",
+  "catalogId": "https://example.com/catalogs/custom-v1",
+  "instructions": "Design instructions for LLMs when generating layouts under this catalog.",
+
+  // Rule 1: Top-level components declared under top-level "components" map.
+  "components": {
+    "Text": {
+      "type": "object",
+      // Rule 5: Components must combine ComponentCommon and local properties using "allOf".
+      "allOf": [
+        {
+          // Rule 3: External references must reference standard types in common_types.json.
+          "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/ComponentCommon",
+        },
+        {
+          "type": "object",
+          "properties": {
+            // Rule 4: Required "component" property must be a constant matching the component key.
+            "component": {
+              "const": "Text",
+            },
+            // Leaf properties can be standard JSON primitives or Dynamic wrappers
+            "text": {
+              "$ref": "https://a2ui.org/specification/v1_0/common_types.json#/$defs/DynamicString",
+              "description": "Text content to display.",
+            },
+          },
+          "required": ["component", "text"],
+        },
+      ],
+      "unevaluatedProperties": false,
+    },
+  },
+
+  // Rule 1: Top-level functions declared under top-level "functions" map.
+  "functions": {
+    "required": {
+      "type": "object",
+      "description": "Checks that the value is not null, undefined, or empty.",
+      // Rule 6: Strict function metadata defined outside the properties block.
+      "returnType": "boolean",
+      "callableFrom": "clientOnly",
+      "properties": {
+        // Rule 6: Function call schema requires constant with function's name.
+        "call": {
+          "const": "required",
+        },
+        "args": {
+          "type": "object",
+          "properties": {
+            "value": {
+              "description": "The value to check.",
+            },
+          },
+          "required": ["value"],
+          "additionalProperties": false,
+        },
+      },
+      "required": ["call", "args"],
+      "unevaluatedProperties": false,
+    },
+  },
+
+  // Rule 1 & Rule 2: $defs is restricted strictly to surfaceProperties, anyComponent, and anyFunction.
+  // Custom definitions or helpers inside a catalog are strictly prohibited under $defs.
+  "$defs": {
+    "surfaceProperties": {
+      "type": "object",
+      "properties": {
+        "agentDisplayName": {
+          "type": "string",
+        },
+      },
+    },
+    "anyComponent": {
+      "oneOf": [
+        {
+          // Rule 3: Local refs restricted to top-level components map.
+          "$ref": "#/components/Text",
+        },
+      ],
+      "discriminator": {
+        "propertyName": "component",
+      },
+    },
+    "anyFunction": {
+      "oneOf": [
+        {
+          // Rule 3: Local refs restricted to top-level functions map.
+          "$ref": "#/functions/required",
+        },
+      ],
+    },
+  },
+}
+```
+
 ### UI composition: the adjacency list model
 
 The A2UI protocol defines the UI as a flat list of components. The tree structure is built implicitly using ID references. This is known as an adjacency list model.
diff --git a/specification/v1_0/json/client_capabilities.json b/specification/v1_0/json/client_capabilities.json
index 9c2635076..3d1a0d1c2 100644
--- a/specification/v1_0/json/client_capabilities.json
+++ b/specification/v1_0/json/client_capabilities.json
@@ -101,7 +101,29 @@
       "properties": {
         "$schema": {"type": "string"},
         "$id": {"type": "string"},
-        "$defs": {"type": "object"},
+        "$defs": {
+          "type": "object",
+          "description": "Standardized schema definitions referenced from outside the catalog file.",
+          "properties": {
+            "surfaceProperties": {
+              "title": "A2UI Surface Properties Schema",
+              "description": "A JSON Schema that defines the catalog's surface properties.",
+              "$ref": "https://json-schema.org/draft/2020-12/schema"
+            },
+            "anyComponent": {
+              "title": "A2UI Any Component Schema",
+              "description": "Unified validation schema for all components.",
+              "$ref": "https://json-schema.org/draft/2020-12/schema"
+            },
+            "anyFunction": {
+              "title": "A2UI Any Function Schema",
+              "description": "Unified validation schema for all functions.",
+              "$ref": "https://json-schema.org/draft/2020-12/schema"
+            }
+          },
+          "required": ["anyComponent", "anyFunction"],
+          "additionalProperties": false
+        },
         "title": {
           "type": "string",
           "description": "The title of the catalog."
@@ -131,14 +153,6 @@
           "additionalProperties": {
             "$ref": "#/$defs/FunctionDefinition"
           }
-        },
-        "surfaceProperties": {
-          "title": "A2UI Surface Properties",
-          "description": "A schema that defines a catalog of A2UI surface properties. Each key is a surface property name, and each value is the JSON schema for that property.",
-          "type": "object",
-          "additionalProperties": {
-            "$ref": "https://json-schema.org/draft/2020-12/schema"
-          }
         }
       },
       "required": ["catalogId"],