Understanding Success Criterion 2.5.2: Pointer Cancellation

Success Criterion 2.5.2 Pointer Cancellation (Level A): 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.

Functions that emulate a keyboard or numeric keypad key press are considered essential.

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).

Intent

The intent of this success criterion is to make it easier for users to prevent accidental or erroneous pointer input. People with various disabilities can inadvertently initiate touch or mouse events with unwanted results. Each of the following subsections roughly aligns with the bullets of this Success Criterion, and outlines a means of allowing users to cancel pointer operations.

Up-Event activation or completion

The most accessible way to incorporate pointer cancellation is to make activation occur on the up-event.

Up-event activation refers to the activation of a target when the pointer is released. In a touchscreen interaction, when the finger touches a target, the up-event activation only occurs when the finger is lifted while still being within the target boundary. Similarly in mouse interaction, the up-event occurs when the mouse button is released while the cursor is still within the boundary of the initial target set when the mouse button was pressed.

Authors can reduce the problem of users inadvertently triggering an action by using generic platform activation/click events that activate functionality on the up-event. For example, the click event in JavaScript triggers on release of the primary mouse button, and is an example of an implicit up-event. Despite its name, the click event is device-independent and also works for touch and keyboard interaction.

The preference for up-events is implicit in the Success Criterion wording of the first bullet: The down-event of the pointer is not used to execute any part of the function. Authors meet the first bullet by using only the up-event.

Up-Event Abort or Undo

Where the interaction is equivalent to a simple "click", up-event activation has a built-in ability to cancel. There is a distinction between when someone touches a screen and when they remove their finger. Similarly, in mouse interaction, there is a difference between pressing and releasing the mouse button. When activation occurs only as the pointer is released, users have the opportunity to Abort (cancel) the activation. Users who have difficulty accurately using a mouse or touchscreen benefit greatly from this basic behaviour. They normally receive visual feedback when an item is pressed. If they discover they have selected the wrong item, they can cancel the action by moving their pointer or finger away from the target before releasing.

For more complex interactions, such as drag and drop, the down- and up-events may initiate and end a series of actions to complete a process. For example, with drag and drop, the item may be:

  1. selected with a press (down-event),
  2. moved to a new location, while still being depressed, and
  3. released (up-event) to conclude the drop action.

In such a complex action, the need for an Abort or Undo function increases. Designers may elect to confirm the move through something like a confirmation dialog or an undo button, giving the user the ability to Undo the process just completed. Alternatively, the ability to Abort the action can be acheived if, before completing step 3, the user returns the selected item to its original location and concludes the process there. If other parts of the screen disallow a move, the user can conclude the drag and drop there, effectively nullifying the operation.

Up Reversal

In other interactions, the down-event may trigger a behaviour which can be reversed when the up-event concludes. Examples of this include press-and-hold actions such as where a transient popup appears (or a video plays) when the user presses on an object (down-event), but the popup (or video) disappears as soon as the user releases the pointer (up-event). Since the up-event reverses the preceding down event, the user is returned to their prior point, and has effectively cancelled the operation.

Down-Event

Completing the function on the down-event is only permitted when it is essential that the up-event not be used.

The most prevalent essential down-event activation occurs in keyboard emulation. On a physical keyboard, keys by default activate on the down-event -- a letter appears when the key is pressed. If a software keyboard emulator tried to override this expected behaviour by making letters appear when the key is released, the behaviour would be unexpected and would adversely affect expected interaction.

Note that a keyboard has a built-in Backspace or Delete button, which effectively provides an Undo option. Undo is not a requirement of the down-event Essential exception; however, providing an easy way for users to undo any action is a recommended practice (and may be a functional necessity), even where it is not a requirement of this Success Criterion.

Other examples where the timing of an activation is essential and requires the down-event would be:

  • An activity that emulates a physical on-press trigger, such as when playing an on-screen piano keyboard. Activation on the up-event would significantly alter the desired behaviour.
  • A program for shooting skeets where waiting for the "up" event would invalidate the precise timing necessary for the activation.

Benefits

Examples

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques

Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. However, it is not necessary to use these particular techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.

Sufficient Techniques

Advisory Techniques

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.

Failures

The following are common mistakes that are considered failures of this Success Criterion by the WCAG Working Group.

Key Terms

down-event

new

platform event that occurs when the trigger stimulus of a pointer is depressed

The down-event may have different names on different platforms, such as "touchstart" or "mousedown".

essential

if removed, would fundamentally change the information or functionality of the content, and information and functionality cannot be achieved in another way that would conform

functionality

processes and outcomes achievable through user action

mechanism

process or technique for achieving a result

The mechanism may be explicitly provided in the content, or may be relied upon to be provided by either the platform or by user agents, including assistive technologies.

The mechanism needs to meet all success criteria for the conformance level claimed.

single pointer

new

pointer input that operates with one point of contact with the screen, including single taps and clicks, double-taps and clicks, long presses, and path-based gestures

up-event

new

platform event that occurs when the trigger stimulus of a pointer is released

The up-event may have different names on different platforms, such as "touchend" or "mouseup".