Re: emacs rendering comparisson between emacs23 and emacs26.3

[Stefan Monnier]

> The doc string of jit-lock-contextually says:
>
>   If t, means fontification occurs on those lines modified and all
>   subsequent lines.  This means those subsequent lines are refontified to 
> reflect
>   their new syntactic context, after `jit-lock-context-time' seconds.
>   If any other value, e.g., `syntax-driven', means syntactically true
>   fontification occurs only if syntactic fontification is performed using the
>   buffer mode's syntax table, i.e., only if `font-lock-keywords-only' is nil.
>
> 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.

> 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.


        Stefan