Merge block 0x0001_???? into block 0x0000_????

doc/articles/Extensions.md

@@ -48,14 +48,15 @@ Note also:
 
 ## Registry of prefixes and enum blocks
 
-Implementation extensions **should**, and multi-implementation extensions **must**, use the naming conventions listed above with the prefixes listed here.
+Implementation-specific extensions **should** use the naming conventions listed above, with the name prefixes listed here.
 
-Implementation-specific and multi-implementation extensions **must** not use block `0x0000_????` when adding values to existing enums.
+Implementation-specific extensions **must** use their assigned block when adding new values to existing enum types. (Implementation-specific enum types do not need to use these blocks since they are exclusive to one implementation.)
+
+If an implementation does not have an assigned prefix and block, it **should** be added to this registry.
 
 |                      | Prefix       | Enum Block    | Description
 |----------------------|--------------|---------------|------------
-| Core                 | (none)       | `0x0000_????` | Extensions that are required to implement, e.g. added after 1.0.
-| Multi-Implementation | (none)       | `0x0001_????` | Extensions that are optional to implement (unless otherwise specified as required), e.g. platform-specific extensions.
+| Standard             | (none)       | `0x0000_????` | Extensions standardized in webgpu.h
 | Compatibility Mode   | *TBD*        | `0x0002_????` | **Special:** implementations that don't support Compatibility Mode must ignore any chained structs with @ref WGPUSType values in this block, instead of erroring. This block must only be used for Compat additions that can be ignored without affecting the semantics of a non-erroring program.
 | wgpu-native          | `Wgpu`       | `0x0003_????` |
 | Emscripten           | `Emscripten` | `0x0004_????` |