Re: display property as display spec vector behavior unclear

[Johan Bockgård]

Joe Wells <jbw@macs.hw.ac.uk> writes:

> The documentation in the Emacs Lisp manual on the display property
> states this:
>
>   The value of the `display' property should be a display
>   specification, or a list or vector containing several display
>   specifications.
>
> Unfortunately, this is the only thing it states about the case where
> the display property is a list or vector of display specs.
> I searched for all occurrences of the words “list” and “vector” in
> that section of the manual and could not find more precise details.
>
> I would guess from the above description that if the display property
> were a vector of display specs, then all of the things specified to be
> displayed would be shown from left to right.  However, it seems that
> only the first one is used, which seems strange.

A vector or list is used for combining properties (where is makes
sense), not laying things out in sequence.

This passage from the comment of handle_single_display_spec is
relevant:

    DISPLAY_REPLACED_P non-zero means that we previously saw a
    display specification which already replaced text display
    with something else, for example an image; we ignore such
    properties after the first one has been processed.

Properties that don't "replace text with something else" include
`height', `raise', `space-width'. These can be combined.

Image slices use `slice' together with `image'.

-- 
Johan Bockgård