Re: Nested display strings

[Andreas Röhler]

Am 23.04.2011 18:44, schrieb Eli Zaretskii:
> The following 4 lines define two overlays with display strings, with
> the second overlay "nested" inside the first one:
>
> (defvar myov1 (make-overlay 16 51))
> (overlay-put myov1 'display "STRING1")
> (defvar myov2 (make-overlay 29 43))
> (overlay-put myov2 'display "STRING2")
>
> If you evaluate this in the *scratch* buffer, the result is this:
>
> ;; This buffer STRING1STRING2STRING1, and for Lisp evaluation.
>
> That is, STRING1 is displayed twice!  Is this a bug or a feature?
>
> I asked Gerd Möllmann, and he told me that this is an accident: what
> he really meant was, once STRING1 is displayed, to skip to the end of
> its overlay, so that the nested overlay myov2 would not be displayed
> at all.
>
> However, after so many years (this is how Emacs behaves since v21.1),
> perhaps we should keep this behavior.  Does anyone know any real-life
> use cases where this "feature" is needed or would be beneficial?
>
> The reason I'm asking is that whether we keep or remove this feature
> affects the detailed design of how bidirectional text should be
> reordered in the presence of display properties and overlay strings.

Hi,

would consider it definitly a bug with respect of
following order of evaluation:

(defvar myov2 (make-overlay 29 43))
(defvar myov1 (make-overlay 16 51))
(overlay-put myov2 'display "STRING2")
(overlay-put myov1 'display "STRING1")

ie if the wider overlay is applied last, it should take all.

Cheers

Andreas