For triggering actions (which includes normal typing), you only ever use keydown.
I think you have this wrong, actions generally occur on button release, until that you can move the mouse cursor to a different target, tab to another control, use [ESC] to cancel, and so on. Typing, moving a slider with the cursor keys, and similar things that make use of key repetition while holding down the key are the exception to this.
I am speaking specifically of keyboards. For mice, it’s release. (When I made a similar comment two months ago on Lobsters when this article came up there, I mentioned this, but decided to leave it out this time, thinking the context was clear enough. I think I was wrong.)
Can you give some specific examples? In my experience (which I also verified to make sure), all of the things you mention act on keydown. The exceptions are on multi-key combinations, which follow a special key that is held down while modifiers are entered, where the action is completed by releasing this special key (ALT + TAB [...TAB | SHIFT]) being a common example.
TAB is otherwise immediate, as is ESC, and the examples of typing, as well. So I'm left wondering, how do they have it wrong?
> all of the things you mention act on keydown
Because they listed the exceptions to the "act on keyup" rule
If only one case follows your rule, and everything else ever implemented from the start of personal computers is an exception, your rule is awry.
The GP means that, if you hold space down on a button, you can then tab to another button without activating the first one.