Re: emacs rendering comparisson between emacs23 and emacs26.3

[Eli Zaretskii]

> From: Stefan Monnier <address@hidden>
> Cc: address@hidden,  address@hidden,  address@hidden,
>   address@hidden,  address@hidden,  address@hidden
> Date: Wed, 08 Apr 2020 10:22:29 -0400
> 
> > I understand what t means and does, but what does non-nil, non-t value
> > do, and how is it different from t?
> 
> This is a global variable.  The non-nil non-t value means "treat it as
> nil in some buffers and as t in others, depending on
> `font-lock-keywords-only`" (well, more or less: other users of jit-lock
> than font-lock can also affect it, but as a first approximation that's
> about it).
> 
> > in particular, does it also wait for jit-lock-context-time
> > of idleness?
> 
> Yes.

Thanks.

> > The code doesn't seem to start the jit-lock-context-timer if the value
> > is non-t, or am I missing something?
> 
> Yes, you're missing:
> 
>     (when (and contextual jit-lock-contextually)
>       (setq-local jit-lock-contextually t))
> 
> which will turn the non-nil non-t value into t when applicable.

This is in jit-lock-register, which is not called from jit-lock.el.
Does this mean that non-nil, non-t value of jit-lock-contextually is
like nil, unless the major mode calls jit-lock-register with its 2nd
argument non-nil?  And if so, why does the doc string mention
font-lock-keywords-only and doesn't mention jit-lock-register?  They
seem to be at least theoretically independent?  If not, where's their
connection?