For functionality that can be operated using a single pointer, completion of the function is on the up-event with an ability to abort, undo or reverse the outcome. (Level A)

Rationale

Objective: Reduce accidental activation of controls by making their operation consistent

This checkpoint is intended to benefit a range of users with cognitive, physical or visual disabilities. Authors (especially developers, for whom this checkpoint is most relevant) who follow its requirements will help ensure that pointer operation is predictable and consistent. To prevent accidental or erroneous pointer input, ensure 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

If users mistakenly activate a mouse button or touchscreen, or if they have poor fine motor control and click the wrong thing, they can cause unintended consequences. Therefore the intention of this checkpoint is that the incidence of accidental activation can be diminished and the effects lessened.

If no down-event causes execution, a user who mistakenly clicks a control does not immediately activate the control. Instead, activation occurs on the up-event when the user releases the control (e.g., by taking their finger off the mouse button or the touchscreen). This provides users with an opportunity to nullify their action, for instance by moving the pointer away from the control. Moving the pointer away from the target while the mouse button is still depressed, then releasing the pointer when it is no longer over any control, is a built-in example of the ability to abort on the up-event.

A drag-and-drop operation that completes on the up-event and then asks for confirmation to move the object is an example of an undo function. A help icon that displays a message when pressed (on the down-event) that then disappears when it is no longer pressed (on the up-event) is an example of up reversal. Finally, a piano keyboard emulator is an example of a function that is down-event essential. A physical piano plays a note when the piano key is pressed, and any emulator must also do so to approximate the experience.

IBM has simplified the normative language of this checkpoint. Refer to Understanding 2.5.2 (external link to WCAG) for more information.

Development Techniques

This paragraph appears generically in all checkpoints. Review the General techniques as well as other tabs applicable to your technology.  Prioritize the use of technology-specific techniques, and implement the General techniques as needed. You are always required to find, understand and implement accessible code techniques to meet the checkpoint. The documented techniques and supplements are not exhaustive; they illustrate acceptable ways to achieve the spirit of the checkpoint. If numbered, techniques are in order of preference, with recommended techniques listed first. Where used, IBM information that complements the WCAG techniques is indicated as supplemental.

General techniques

Where applicable, any item in this section represents a technique deemed sufficient. Ensure you review WCAG Common Failures to avoid development mistakes.

Web (HTML, ARIA, CSS) techniques

In addition to the General techniques, any item in this section represents a technique deemed sufficient.

Mobile Native (iOS) techniques

There are no specific Mobile Native iOS techniques for this checkpoint. Refer to the General techniques section.

Eclipse techniques

There are no specific Eclipse techniques for this checkpoint. Refer to the General techniques section.

Windows-based (MSAA+IA2) techniques

There are no specific Windows-based (MSAA+IA2) techniques for this checkpoint. Refer to the General techniques section.


Many links in this checklist reside outside ibm.com at the Web Content Accessibility Guidelines (WCAG) 2.1. W3C Recommendation 05 June 2018: http://www.w3.org/TR/WCAG21/

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