> Thanks, but I'm not sure yet how to connect this to what the display
> engine actually does.  Are you familiar with what happens in the
> display code during a single redisplay cycle?  If so, could you
> describe that and insert into that description what you say above?
> That would go a long way towards making sure we are on the same page,
> which I think is a necessary precondition for discussing your
> proposal.
>
I admit I don't know about the internal working of the display engine.

Failing that, I could try asking questions whose answers might help
> reconstructing those missing links.  For example:
>
>  . does this mean you expect the display engine to tell that
>    display-svg-hook which parts of the display were redrawn?
>
No, that won't be necessary. After change hooks and other APIs are enough
to derive change and context information. In my experience, the characters
around the point are usually the most relevant.

 . what is the "required information" to be passed to
>    display-svg-hook, and how will it be generated from the information
>    that exists in the display engine?
>
 "required information" in my sentence above refers to the parameters of
(svg-render) API viz. svg x y width height. display-svg-hook can be a
no-arg function.