Document the permanent bidirectional stability of immutable ArrayBuffer contents

[gibson042]

No description provided.

[github-actions]

The rendered spec for this PR is available at https://tc39.es/proposal-immutable-arraybuffer/pr/44.

[bakkot]

Grammar?

Suggested change

	<dd>It is used to create an immutable ArrayBuffer (i.e., an ArrayBuffer with a an [[ArrayBufferIsImmutable]] slot) with contents from _fromBlock_. The contents of an immutable ArrayBuffer's Data Block are constrained to be permanently stable, and may not be modified by either ECMAScript code or by other activities that may take place inside an implementation or observable by it.</dd>
	<dd>It is used to create an immutable ArrayBuffer (i.e., an ArrayBuffer with a an [[ArrayBufferIsImmutable]] slot) with contents from _fromBlock_. The contents of an immutable ArrayBuffer's Data Block are constrained to be permanently stable, and may not be modified by either ECMAScript code or by other activities that may take place inside an implementation or be observable by it.</dd>

[devsnek]

Is it not that the contents must never be observably modified, specifically from the perspective of ecmascript code? in practice that would still mean the host can't modify the backing memory.

[bakkot]

This is strictly speaking normative. (I claimed otherwise earlier but was mistaken.)

[erights]

Given @bakkot 's later point, that the rest of the spec as a whole still does not imply immutability, and therefore that this change is normative, I'm removing the term "Editorial: " from the title.

[gibson042]

This merge was somehow lost, and has been restored as 83479c9.

[erights]

I might have lost it with late-night "git push --force" steps when, in retrospect, I was too tired to do such things. Sorry!

If you can, please check if I accidentally wiped out anything else. Thanks!

[gibson042]

All of the other PRs seem to still be in place, but direct pushes to main are harder to track. I did just open #45, which may or may not duplicate a prior addition.

[mhofman]

https://github.com/tc39/proposal-immutable-arraybuffer/activity?ref=main only shows a single force push that doesn't seem to have erased anything.