bug#34794: 26.1; doc of `read-buffer'

[Drew Adams]

> > AFAICT neither the doc string nor the Elisp manual states what the
> > default value is if argument DEF is nil.  IOW, what is the default
> > buffer name if no explicit default is provided?  It seems (without
> > thorough testing) to be the value of `(buffer-name (current-buffer))'.
> 
> No, it's an empty string, and I think the doc string already conveys
> that.

I cannot tell from the doc string that the default value,
i.e., the value returned when DEF is nil, is the empty
string.  I don't see how/where the doc string conveys
that at all.  AFAICT, one would need to consult the C
source code to find that info.

Where in the doc string do find the info that a nil
value of DEF returns "" if the user enters an empty
line?  Where do you see that stated or even implied?

> (Note that if read-buffer-function is non-nil, what happens
> then is entirely up to that function, which doesn't make it easy to
> say exactly how DEF is handled.)

It's not hard to state what the default DEF behavior
is, and then later say that if `read-buffer-function'
is non-nil then the use of the other args is up to it,
i.e., not necessarily as described above.  This is
not unusual for a function that optionally accepts a
function arg as one possibility.