Re: Question: add-face-text-property for 'font-lock-face?

[Qiantan Hong]

> You want font-lock-append-text-property, I think:
> 
>  (font-lock-append-text-property START END PROP VALUE &optional OBJECT)

I think rather than hardcode a C function for another property, we could just
expose the general function the C implementation now is internally using
(add-text-property-1 START END PROP OBJECT MODE DESTRUCTIVE)

However, sorry for my own confusion, I found out this actually doesn’t solve my 
problem.
Recall the problem:
> Users of crdt.el report that crdt-visualize-author-mode (which use 
> font-lock-face to color code author of texts)
> conflict with faces from other modes. Apparently there are more than 1 mode 
> which sets this text property.
In fact in most cases those other mode doesn’t set the ‘font-lock-face property,
the problem is ‘font-lock-face property (aka recalculated fontification) I set 
overrides other font lock mechanism.

Is there a right way to add attributes while preserving font lock faces from 
other mode?
I now see that Yuan’s suggestion of overlay will do this, but there’s 
performance concern.