For functionality that can be operated using a single pointer, at least one of the following is true:
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.
Note 1
Functions that emulate a keyboard or numeric keypad key press are considered essential.
Note 2
This requirement applies to web content that interprets pointer actions (i.e., this does not apply to actions that are required to operate the user agent or assistive technology).
Single finger or cursor interactions can be cancelled or undone.