And on the mobile site (like https://m.xkcd.com/538/ https://m.xkcd.com/538/) the text "alt-text" itself is a clickable link that toggles display of the alt-tex

And on the mobile site (like https://m.xkcd.com/538/ https://m.xkcd.com/538/) the text "alt-text" itself is a clickable link that toggles display of the alt-text on and off. (Not reachable by tab key, though, for some reason.)