Guidance for proposals around new global constructors

[ptomato]

As per the May 2021 plenary (https://github.com/tc39/notes/blob/master/meetings/2021-05/may-26.md#discussion-of-globals-and-guidance-for-future-proposals), this repo should contain a document providing guidance to future proposals that want to introduce new global constructors / namespaces.

[ptomato]

One thing not mentioned in the plenary which could go in the guidance, is whether namespace objects should have a [@@toStringTag] property. Seems more helpful than harmful? See tc39/proposal-temporal#1539 (comment)

[bakkot]

whether namespace objects should have a [@@toStringTag] property

Yes, per the July 2020 meeting (see tc39/ecma262#2057).

[ljharb]

The more specific question is, is that just top-level ones, or all? iow, Temporal surely must, per that consensus - but what about Temporal.now?