>> > This is a related option, but I'm not sure if it should be mentioned
>> > in the docstring.  Maybe a simple reference should be sufficient?
>> 
>> I think mentioning it in the `yes-or-no-p' doc string would be good.
>
> I think that the doc for this option should explicitly discourage
> using the value that abbreviates, and say why.
>
> It should say that `yes-or-no-p' is _intended_ to be used when it's
> thought that you should not respond too quickly.  At least point that
> out, for users to think about before customizing.

Thanks for suggestions.  Now below is a new patch with these changes.

> Presumably this option is being added because there are apparently
> a lot of users who don't want to be slowed down by `yes-or-no-p'.
> But that's exactly the point of `yes-or-no-p'.

For many users using longer answers doesn't protect from mistakes.
Sometimes I execute a command without verifying if it's right,
e.g. first running a harmless command, then a more dangerous,
then I forget about the last command, and thinking that the last one
was the harmless command, quickly type a key sequence 'M-! M-p RET'.