Fast spell-checking in Emacs with Jinx

Emacs has had a spell-checker for a very long time. In fact, I’ve been using ispell-word for at least several years now, as I have mentioned for example here. However, I’ve only used Flyspell mode once, over two decades ago, when I tried it out on a machine with maybe 8MB RAM and a Pentium-class processor clocked at about 100MHz and decided that it’s too slow to be really useful. Well, things have changed a bit since then, haven’t they?