>From: Brendan Eich [mailto:brendan@...]
>> BTW, I haven't yet perceived that we have consensus on putting this
>> into ES5. My interpretation of Brendan's initial comments on the
>> matter was that he was opposed to it for ES5. (I'm sure he'll let
>> us know whether or not that is correct).
>It's late in the game, but a sentence about [[Prototype]] seems
>doable. I defer to you on this, since you're Editor and it'll fall
>upon you to draft the change.
OK, I'll put it in. Here is what I am inserting into section 8.6.2 following the paragraph about [[Prototype]] that comes immediately after table 4:
Every ECMAScript object has a Boolean-valued [[Extensible]] internal property that controls whether or not named properties may be added to the object. If the value of the [[Extensible]] internal property is false then additional named properties may not be added to the object. In addition, if [[Extensible]] is false the value of the [[Prototype]] internal property of the object may not be modified. Once the value of an [[Extensible]] internal property has been set to false if may not be subsequently changed to true.
This specification defines no ECMAScript language operators or built-in functions that permit a program to modify an object's [[Prototype]] internal property or to change the value of [[Extensible]] from false to true. Implementation specific extensions that modify [[Prototype]] or [[Extensible]] must not violate the invariants defined in the preceding paragraph.