extensionsRequired property

specification/README.md

@@ -39,6 +39,7 @@ Copyright (C) 2013-2016 The Khronos Group Inc. All Rights Reserved. glTF is a tr
   * [Animations](#animations)
   * [Metadata](#metadata)
   * [Specifying Extensions](#specifying-extensions)
+    * [Specifying GL Extensions](#specifying-gl-extensions)
 * [Properties Reference](#properties)
 * [Acknowledgements](#acknowledgements)
 * [Appendix A: Default Material](#appendix-a)
@@ -1123,25 +1124,50 @@ Only the `version` property is required. For example,
 
 glTF defines an extension mechanism that allows the base format to be extended with new capabilities. Any glTF object can have an optional `extensions` property, as in the following example:
 
-```javascript
-"a_shader": {
+```json
+{
+  "a_shader": {
     "extensions": {
-        "binary_glTF": {
-            "bufferView": // ...
-        }
+      "KHR_binary_glTF": {
+        "bufferView": "a_shader_bufferView"
+      }
     }
+  }
 }
 ```
 
-All extensions used in a model are listed in the top-level `extensionsUsed` dictionary object, e.g.,
+All extensions used in a glTF asset are listed in the top-level `extensionsUsed` dictionary object, e.g.,
 
-```javascript
-"extensionsUsed": [
-   "KHR_binary_glTF"
-]
+```json
+{
+  "extensionsUsed": [
+    "KHR_binary_glTF", "VENDOR_physics"
+  ]
+}
+```
+
+All glTF extensions required to load and/or render an asset must be listed in the top-level `extensionsRequired` dictionary object, e.g.,
+
+```json
+{
+  "extensionsRequired": [
+    "KHR_binary_glTF"
+  ]
+}
 ```
 
-_TODO: add note on how this is different than `glExtensionsUsed` property._
+<a name="specifying-gl-extensions"></a>
+### Specifying GL extensions
+
+If loading an asset requires enabling GL extensions to provide functionality beyond used profile (e.g., WebGL 1.0), such extensions must be listed in the top-level `glExtensionsUsed` dictionary object, e.g.,
+
+```json
+{
+  "glExtensionsUsed": [
+    "OES_element_index_uint"
+  ]
+}
+```
 
 For more information on glTF extensions, consult the [extensions registry specification](../extensions/README.md).
 
@@ -2049,6 +2075,7 @@ The root object for a glTF asset.
 |**techniques**|`object`|A dictionary object of [`technique`](#reference-technique) objects.|No, default: `{}`|
 |**textures**|`object`|A dictionary object of [`texture`](#reference-texture) objects.|No, default: `{}`|
 |**extensionsUsed**|`string[]`|Names of glTF extensions used somewhere in this asset.|No, default: `[]`|
+|**extensionsRequired**|`string[]`|Names of glTF extensions required to properly load this asset.|No, default: `[]`|
 |**glExtensionsUsed**|`string[]`|Names of WebGL extensions required to render this asset.|No, default: `[]`|
 |**extensions**|`object`|Dictionary object with extension-specific objects.|No|
 |**extras**|`any`|Application-specific data.|No|
@@ -2208,6 +2235,14 @@ Names of extensions used somewhere in this asset.
    * Each element in the array must be unique.
 * **Required**: No, default: `[]`
 
+### glTF.extensionsRequired
+
+Names of glTF extensions required to properly load this asset.
+
+* **Type**: `string[]`
+   * Each element in the array must be unique.
+* **Required**: No, default: `[]`
+
 ### glTF.extensions
 
 Dictionary object with extension-specific objects.

specification/schema/glTF.schema.json

@@ -14,6 +14,15 @@
             "uniqueItems" : true,
             "default" : []
         },
+        "extensionsRequired" : {
+            "type" : "array",
+            "description" : "Names of glTF extensions required to properly load this asset.",
+            "items" : {
+                "type" : "string"
+            },
+            "uniqueItems" : true,
+            "default" : []
+        },
         "accessors" : {
             "type" : "object",
             "description" : "A dictionary object of accessors.",