Require depth clear value in 0.0-1.0 (gpuweb#2421)

* Require depth clear value in 0.0-1.0

* clarify handling of union

spec/index.bs

@@ -7266,11 +7266,13 @@ dictionary GPURenderPassDepthStencilAttachment {
 
     : <dfn>depthLoadValue</dfn>
     ::
-        If a {{GPULoadOp}}, indicates the load operation to perform on
+        If this is a {{GPULoadOp}}, it indicates the load operation to perform on
         {{GPURenderPassDepthStencilAttachment/view}}'s depth component prior to
         executing the render pass.
-        If a `float`, indicates the value to clear {{GPURenderPassDepthStencilAttachment/view}}'s
+
+        Otherwise, this is a `float` indicating the value to clear {{GPURenderPassDepthStencilAttachment/view}}'s
         depth component to prior to executing the render pass.
+        Must be between 0.0 and 1.0, inclusive. <!-- unless unrestricted depth is enabled -->
 
         Note: It is recommended to prefer a clear-value; see {{GPULoadOp/"load"}}.
 
@@ -7317,6 +7319,8 @@ dictionary GPURenderPassDepthStencilAttachment {
          a single [=mipmap level=], single [=array layer=], and all the [=aspects=] in the texture.
     - |this|.{{GPURenderPassDepthStencilAttachment/view}}.{{GPUTexture/[[descriptor]]}}.{{GPUTextureDescriptor/usage}}
         must contain {{GPUTextureUsage/RENDER_ATTACHMENT}}.
+    - If |this|.{{GPURenderPassDepthStencilAttachment/depthLoadValue}} is a clear value (has type `float`),
+        it must be between 0.0 and 1.0, inclusive. <!-- unless unrestricted depth is enabled -->
     - If |this|.{{GPURenderPassDepthStencilAttachment/view}}.{{GPUTextureView/[[descriptor]]}}.{{GPUTextureViewDescriptor/format}}
         is a [=combined depth-stencil format=]:
         - |this|.{{GPURenderPassDepthStencilAttachment/depthReadOnly}} must be equal to |this|.{{GPURenderPassDepthStencilAttachment/stencilReadOnly}}