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Emacs: public test for my 'dired-preview' package

This is a simple package to automatically preview in a side window the file at point in Dired buffers. Preview windows are closed when they are no longer relevant, while preview buffers are killed if they have not been used for other purposes beside previewing.

Enable the dired-preview-mode in the current Dired buffer and then perform the regular up/down motions (n or p with default key bindings) to call the commands dired-preview-next-file, dired-preview-previous-file. Those will trigger the preview.

The previewed file is displayed in a side window if its size is below the number specified in the user option dired-preview-max-size. Previews are shown subject to a small delay, per ther user option dired-preview-delay.

Files matching the dired-preview-ignored-extensions-regexp are not previewed. The default value of that user option includes multimedia, PDFs, and EPUBs.

[ In the future, we may find ways to quickly preview any file type without affecting the performance of Emacs. Though dired-preview is designed to have no external dependencies, so such an ambition may not be realisable (e.g. produce a thumbnail out of a video). ]

To set up dired-preview-mode in every Dired buffer, set it up thus:

(add-hook 'dired-mode-hook #'dired-preview-mode)

I took inspiration for dired-preview from the now-unmaintained peep-dired package by Adam Sokolnicki: https://github.com/asok/peep-dired. My original plan was to volunteer to maintain peep-dired but I decided to write it my own way: it was easier for me, plus I can implement only what I consider necessary without upsetting existing users.