bug#16293: 24.3.50; doc of `string-to-number'

[Drew Adams <drew.adams@oracle.com>]

> >> > Say what happens if STRING cannot successfully be parsed as a number:
> >> > the function raises an error.
> >>
> >> When would it give an error, rather than 0?
> >
> > If it never raises an error, then say explicitly that for any
> > string that cannot successfully be parsed as a number it returns 0.
> 
> It does say:
>      If the first character after the ignored whitespace is neither a
>      digit in the given base, nor a plus or minus sign, nor the leading
>      dot of a floating point number, this function returns 0.
>
> Should this be reworded, or perhaps moved to earlier in the
> documentation?

It should be corrected to be more complete.  It's not just about the
first character.  Any string of characters that cannot be successfully
parsed as a number results in a return value of zero (apparently - I
have not checked the code).  "+@", for instance.