Disabled .handle-actions button receives keyboard focus

[alh0319]

The dashboard metaboxes have arrow buttons that allow them to be moved up and down with a keyboard. The top-most metabox has a disabled move up button that is not probramatically disabled so it still receives keyboard focus though it is not functional.

Example:

<button type="button" class="handle-order-higher" aria-disabled="true" aria-describedby="dashboard_site_health-handle-order-higher-description"><span class="screen-reader-text">Move up</span><span class="order-higher-indicator" aria-hidden="true"></span></button>

It would be better if the disabled attribute were added to this button or if it had a negative tab index so that it doesn't receive keyboard focus outside of when the focus is already on it (because it was used to move a meta box into the top-most position).

[alh0319]

This button is also present in the classic editor meta boxes.

[yashjawale]

Thanks @alh0319 for reporting the bug!
I can reproduce this problem, starting work on a patch to fix this...

This PR prevents keyboard focus for dashboard metabox widget arrows which are disabled

Trac ticket: https://core.trac.wordpress.org/ticket/63970

[joedolson]

Only using aria-disabled was intentional at the time. Making the button disabled just introduces other problems, such as a need to move focus when a meta box is moved into an immovable position and causing buttons to disappear when they are not available, rather than just announcing them as disabled.

See: https://core.trac.wordpress.org/ticket/39074#comment:31

Whether something disabled should be totally unavailable or not is a philosophical point: WordPress has generally made the choice that screen readers should be able to perceive disabled fields, rather than hiding them. But this can be re-discussed, certainly.

[joedolson]

Related: #50699. Milestoning for 7.0 along with that, to re-address how these are handled.