Is this proposal about immutability or non-determinism? Or both?

[justingrant]

https://github.com/tc39/proposal-ses#freezing-intrinsics-and-taming-globals says:

To make a transitively immutable root realm, we, respectively

• Remove all non-standard properties
• Remove Math.random
• Remove Date.now
  . . .

Do you mean "immutable" or "non-deterministic"? If the former, then why is Date.now() included? Can the user change the externally-observable state of the Date object by calling Date.now or any other Date method? If the latter, then should the proposal be updated to use "non-deterministic" to match what you mean? If "both" then it's probably worth clearly calling this out in the proposal.

Also: are there use cases where you might want one but not the other? For example, might a test framework want to prevent non-determinism without preventing mutation? Or vice versa, e.g. a plugin framework wishing to prevent mutation but OK with non-deterministic behavior? I'm not very familiar with the use cases so this might be off-target, but I at least wanted to bring up the issue.

Related: #32