Ambiguity in 2.5.2 Pointer Cancellation

[JesusTheHun]

Describe the issue

• No Down-Event: The down-event of the pointer is not used to execute any part of the function;

• Abort or Undo: Completion of the function is on the up-event, and a mechanism is available to abort the function before completion or to undo the function after completion;

• Up Reversal: The up-event reverses any outcome of the preceding down-event;

• Essential: Completing the function on the down-event is essential.

The second element of the list says :

Abort or Undo: Completion of the function is on the up-event, and a mechanism is available to abort the function before completion or to undo the function after completion;

I believe it should be :

Completion of the function is on the down-event

To confirm my believe I checked the example of failure F101 that says :

It is possible to use the down event and mitigate potential issues to avoid failing the Success Criterion. For example, provide a method to easily undo or abort the functionality, or reverse the outcome on the up-event (when the mouse button is released, or when the finger or stylus are lifted from the touchscreen).

IHMO this leaves no ambiguity : being able to easily undo or abort the functionality after executing a function on a down-event passes the success criterion.
But then on the same page, in the tests procedure, there is no check on the undo functionality.

URL
https://www.w3.org/WAI/WCAG22/quickref/?versions=2.1#pointer-cancellation

Recommended solution
One of the following should be done :

1. If it is an error, change up-event for down-event and update the tests procedure to add a check on reversibility
2. If it is not an error, add a more complete description, ideally an exemple of an undo or abort functionality with in the context of an up-event.

Additional context
In our case, we would like to filter a list when the user presses a button. To improve the perceived responsiveness, we would like to use a down-event.
The filter can be removed immediately with click on the same button.
We feel these conditions pass the Success Criterion 2.5.2 but are unsure of our interpretation of the criterion.

[mraccess77]

I believe it was meant to be up-event - because the wording says "completion of the function". The understanding document seems to cover situations that explain interactions where both events may be used - down begins activation of something and up cancels it.