Need algorithm for how focus events are fired

[garykac]

We need a algorithmic description of how focus events are fired.

blur, focus, focusin, focusout

It should also cover: DOMFocusIn and DOMFocusOut

Starting point:

<User shifts focus>
1	focusin	Sent before first target element receives focus
2	focus	Sent after first target element receives focus
3	DOMFocusIn	(If supported)
<User shifts focus>
4	focusout	Sent before first target element loses focus
5	focusin	Sent before second target element receives focus
6	blur	Sent after first target element loses focus
7	DOMFocusOut	(If supported)
8	focus	Sent after second target element receives focus
9	DOMFocusIn	(If supported)

[garykac]

See https://w3c.github.io/uievents/#events-focusevent-event-order

[domenic]

Likely this would replace either part or all of https://html.spec.whatwg.org/#focus-update-steps. Unsure on the exact best division of labor/specs, but happy to help figure it out.