bug#81491: 30.2; Doc of `image-dired-display-*

> From: "Drew Adams" <[email protected]>
> Cc: <[email protected]>
> Date: Sun, 26 Jul 2026 15:42:43 -0700
> 
> > Before I answer, I need you to try and describe what happens in a
> > modern Emacs when you don't pass that argument.  I suspect that what
> > happens completely removes the need for the argument.
> 
> With Emacs 30.2 I get the error "No buffer named
> *image-dired-display-image*", whether or not I
> provide a prefix arg.
> 
> I added my command, `diredp-image-show-this-file', in
> 2015, and I don't use Emacs with images much, if at all.
> I just tried it now with Emacs 26.3 and 24.5, as well
> as 30.2.
> 
> In 26 with no prefix arg, the image is in a square
> window, shown in a separate frame.  The image is full
> size, and the window/frame is not fit to the window.
> I see the message "Could not resize image".
> 
> In 26 with a prefix arg, the image is still full size,
> but the window/frame has a small height.  Same message.
> 
> If I turn OFF option
> `diredp-image-show-this-file-use-frame-flag' then the
> image window is in the same frame as the Dired buffer
> where I invoke the command.  With the option ON, the
> image window is in a separate frame.  The rest is the
> same: image original size, only the window size (height)
> changes with/without prefix arg.
> 
> In 24 with no prefix arg I get an error: "Invalid image
> specification".  With a prefix arg there's no error but
> there's no image - just a blank (white) buffer, and the
> window has a small height.
> 
> I don't recall which Emacs release was current in 2015,
> when I added the command, but I'm pretty sure it worked
> then, at least with my PC etc.  Of course, that was
> with a different MS Windows, different PC, etc.

What happens if you don't pass the prefix argument to
image-dired-display-image?

(I couldn't try your code, because it's incomplete: some functions it
calls are missing.)