bug#25181: 25.1.90; move-beginning-of-line doesn't move point

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 25181@debbugs.gnu.org
> From: Andreas Röhler <andreas.roehler@easy-emacs.de>
> Date: Tue, 13 Dec 2016 10:25:32 +0100
> 
> >>       (setq first-vis-field-value
> >>         (constrain-to-field first-vis orig (/= arg 1) t nil))
> >>
> >> Here first-vis-field-value is set to orig, i.e. pos 16, where it jumps
> >> back-to, not leaving point at BOL.
> > I'm not sure I understood, but if I did, this is a feature: functions
> > such as beginning-of-line stop moving at field boundaries.
> >
> 
> Hmm, is this reasonable? BOL is a very basic concept. Don't think it 
> should be permitted to be interfered with fields.

The idea is that a Lisp program would use fields only when the
produced effect is what the user would expect.  You see this every day
in action when you type "C-x C-f" and then C-a: point stops at the
beginning of the default directory, without entering the "Find file:"
prompt.  Moving point to BOL in this case would be a nuisance.  (You
can still get to the beginning of line by other means, like C-b.)

That's what fields are all about.  If you don't want this effect,
don't use fields; they are opt-in.