Consideration of keyup event for Polyfill instead of keydown

[jihyerish]

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Migrated from w3c/csswg-drafts#4758
Originally created by @joe-watkins on 08 Feb 2020 00:50 GMT+9

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In the polyfill, keydown event and mouseup event are used for the spatial navigation.

I'm curious to see if there is a great case for leveraging a keydown event as apposed to a keyup event. Keyboard users who may have mobility/dexterity type disabilities could benefit from an event that they have more control over the timing of it being fired. e.g. someone with tremors using a keyboard.

WCAG 2.1 A 2.5.2 Pointer Cancellation currently speaks to this concept for touch/mouse. (should clearly extend to keyboard events IMO)
https://www.w3.org/WAI/standards-guidelines/wcag/new-in-21/#252-pointer-cancellation-a

Browser manufacturers may be looking to the polyfill for guidance and I was interested in seeing if maybe a keyup event could be the default vs requiring an override.

https://wicg.github.io/spatial-navigation/#handling-browser-events

[jihyerish]

@joe-watkins, thanks for raising this issue.

I think your opinion is reasonable when thinking of an accessibility point of view.
Other than people who may have mobility/dexterity disabilities, sometimes people can keep pressing an arrow key unintentionally.
In this situation, the focus will keep moving and it would surprise a user.

For now, it won't be a problem to change keydown event to keyup event.
But, just in case, I'll check samples if those are working well or not.