Re: trunk r113878: Refine previous change.

[Glenn Morris]

Juanma Barranquero wrote:

>> These are internal self-defenses of the implementation, we don't
>> expect users to pass such invalid arguments (a.k.a. "undefined
>> behavior") at all.
>
> If they are self defenses, wouldn't be better to signal an error?

I don't think we can go from "this is documented in the manual to work"
to "this is an error" in the space of a day. For now, we can just go to
"this is undocumented", with a view to perhaps making it an error some
years down the line. Cf bug#15059.

> It would break some code, but arguably that code is already broken,
> and silently so.

It's not broken to intentionally make use of documented behaviour,
and we have no way of knowing whether this was being intentionally used
anywhere. (I don't think it matters much.)