The multiple attribute on <select> should pretty much never be used. It’s like the polar opposite of single <select>, where instead of universal familiarity, it has universal unfamiliarity. Perhaps its only saving grace is that I have yet to encounter this attribute in any codebase.

HTML: The Bad Parts

It’s pretty fair to say that everyone knows how to use a native select element. But add that one little attribute, <select multiple>, and now hardly anyone knows how it works. It turns into a weird box UI that you rarely see, and you just need to know how it works. I had to test, and it seems on my machine holding the shift or command key will allow you turn on/off multiple options, but I wouldn’t be surprised if that varied from machine to machine and keyboard to keyboard, and it’s a totally different look/experience on mobile OSs.