Re: enabling evaporation of overlays

[Masatake YAMATO <jet@xxxxxxxx>]

> The idae is rejected but another idea is suggested by RMS in emacs-devel:
> 
> 	How do you think make evaporate overlay's property t by default(when make-overlay)?
> 
>     That would break many programs.  It is the wrong solution.
> 
>     I think the right fix is in fix_start_end_in_overlays.  When an
>     insertion occurs next to an overlay whose beginning-marker is the
>     advancing kind and whose end-marker is not, the overlay should stay
>     empty.
> 
> I will follow this idea.

I've done this. I hope no backwards overlay in GNU Emacs.
I will inspect overlay usage in widgets next. 

BTW, I found a programming tip in button.el of GNU Emacs.

    ;; Default properties for buttons
    (put 'default-button 'face 'button)
    (put 'default-button 'mouse-face 'highlight)
    (put 'default-button 'keymap button-map)
    (put 'default-button 'type 'button)
    (put 'default-button 'action 'ignore)
    (put 'default-button 'help-echo "mouse-2, RET: Push this button")
    ;; Make overlay buttons go away if their underlying text is deleted.
    (put 'default-button 'evaporate t)
    ;; Prevent insertions adjacent to the text-property buttons from
    ;; inheriting its properties.
    (put 'default-button 'rear-nonsticky t)

    (defun make-button (beg end &rest properties)
    ...
	  (overlay-put overlay 'category 'default-button)
	  ...)

With category property, you can give your own default property of overlays 
made in your lisp code. This will be useful in your code.

Masatake YAMATO