Comment 4 for bug 1938448

Also attaching a mockup image of what I'm expecting from the epub just attached before, showing a tall and narrow dialog with vertically running text (same applies to dialog title). Although the dialog controls are shown as rotated, actually I don't know if it can be done at all.

About the left/right alignment, perhaps it is best to go with the natural alignment specified in writing mode.
vertical-rl: Japanese and Traditional Chinese novels and books.
vertical-lr: Rare. Only used by traditional Mongolian script, and I have zero knowledge about it.