What is pointer cancellation?

Pointer cancellation refers to single pointer functionality. Specifically, the WCAG Pointer Cancellation criterion requires that the up-event or down-event of a single pointer follow one of the following functions:

• "The down-event of the pointer is not used to execute any part of the function;" - So, if you press a button without releasing the pointer, the button should not be activated.
• "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;" - For example, if you're dragging an element across the screen, you can release the element on the up-event to either confirm the new position or to cancel the action.
• "The up-event reverses any outcome of the preceding down-event;" - In this case, if you accidentally press an element and don't want it to activate, then you can reverse this by completing the up-event after moving the pointer away from the element. A common example is a drag-and-drop widget for uploading files where a user who's dragged a file (the down-event) into the widget can avoid activating the upload function by dropping the file (the up-event) outside of the widget.
• "Completing the function on the down-event is essential."

For step-by-step guides on how to manually test whether your web content conforms to WCAG success criteria, such as criteria related to single pointer functionality, explore the Guided Manual WCAG Audit Tool from Accessible Web.