Re: Error during redisplay

[Richard Stallman]

    I still think it wrong to change the text according to where it is
    displayed.

I agree -- I get a very bad feeling about that.

    As far as I know, text properties are also subject to undo treatment.

That is another good argument.
     
                This would appear to call at most for overlays 

At present, strings cannot have overlays.  And I am not sure
if overlays are really right for this data; just because text properties
have a bad aspect, that doesn't mean overlays don't.

There could be some other internal cache for this.

It calls for more thought.

> So, another way is to re-design the current redisplay engine
> to generate a composition glyph every time just by calling C
> functions.  I think it's an interesting experiment.

That is cleaner, for sure.  It could also be slower, but how much?