bug#71345: Feature: unleash font-lock's secret weapon; handle Qfontified = non-nil

[JD Smith]

In general, yes.  In my case having the scope be per-buffer not per window makes the most sense in terms of

the functionality.

Given the feature of redisplay I just mentioned, you will actually get

a per-window functionality, at least as far as the position of point

is concerned.

Not in my case, since I am discriminating between point in the selected window and other windows showing the same buffer, such that switching windows = changing point. Since much of the work in my mode is not position-dependent but depends on text content, updating face is the natural thing.  

Thinking more about what makes font-lock “special” as a jit-lock backend, it is exactly this: font-lock claims exclusive ownership of `face'.  Solutions I can see:

1. Make font-lock a good citizen by using its own alias for face. 
2. Give other jit-lock backends which may alter face and potentially conflict with font-lock the ability to specify to jit-lock “if you re-run font lock on a region, re-run me too after that.”