Re: [heycam/webidl] Introduce the observable array type (proxy-based) (#840)

domenic commented on this pull request.



> +        1.  If [=!=] [$IsAccessorDescriptor$](|descriptor|) is <emu-val>true</emu-val>, then return
+            <emu-val>false</emu-val>.
+        1.  If |descriptor| has a \[[Configurable]] field and |descriptor|.\[[Configurable]] is
+            <emu-val>false</emu-val>, return <emu-val>false</emu-val>.
+        1.  If |descriptor| has a \[[Enumerable]] field and |descriptor|.\[[Enumerable]] is
+            <emu-val>false</emu-val>, return <emu-val>false</emu-val>.
+        1.  If |descriptor| has a \[[Writable]] field and |descriptor|.\[[Writable]] is
+            <emu-val>false</emu-val>, return <emu-val>false</emu-val>.
+        1.  If [=!=] [$ToUint32$](|P|) > |oldLen|, return <emu-val>false</emu-val>.
+        1.  Let |idlValue| be the result of [=converted to an IDL value|converting=]
+            |descriptor|.\[[Value]] to the type given by |handler|.\[[Type]].
+        1.  Let |existingDescriptor| be [=!=] [$OrdinaryGetOwnProperty$](|O|, |P|).
+        1.  Assert: |existingDescriptor| is not <emu-val>undefined</emu-val>.
+        1.  Let |existingIDLValue| be the result of [=converted to an IDL value|converting=]
+            |existingDescriptor|.\[[Value]] to the type given by |handler|.\[[Type]].
+        1.  Assert: the above step never throws an exception, since we already went through the

Such a definition does sound nice. The main other use I'd have for it would be saying that such things cannot be used for attributes. (However, probably that's less useful for spec readers than the current architecture, where you can go to the definition of record and have it say right there that it's not allowed as an attribute.)

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