bug#40671: [DOC] modify literal objects

[Drew Adams]

> It's not modification if it's not destructive. At least, in the context
> of the problem we're trying to describe.
> 
> Destructive modification, by itself, is a very regular occasion. Not
> something to warn against.

Whatever.  My point is that there's no need to
scream "Danger!".  A warning does not imply
danger.  And a tip about a gotcha is not
necessarily even a warning.

Can the consequences ever be awful?  Presumably.
Will they often be awful?  Not likely.

The most likely negative effect is spending
time trying to figure out what's happening.
That's why we should have a tip about the
gotcha.