bug#40671: [DOC] modify literal objects

[Drew Adams]

> It seems strange to use the terms "constant" and "mutable" to describe
> whether modifying its contents is something you had better avoid.
> I think people will find that terminology confusing.  Normally
> "mutable" means that you CAN change it, not that it is OK to change it.

Yes.  Precisely what I, Michael, and others said.

The message should be one of advice/guidance:
explaining a gotcha, or at least suggesting what
to avoid.