RE: emacs-27 eebfb72 1/2: Document constant vs mutable objects better

[Drew Adams]

> "mutable" and "safely mutable"/"mutating it is
> a good idea" should be distinguished.

Exactly.

> Similarly here. There are languages, Lisps even, that distinguish
> mutable and immutable strings/conses. In such languages, trying to
> mutate an immutable data structure leads to an error being signalled.
> Conflating "mutable" with "safely mutable" is IMO bound to induce
> confusion.

Ditto.