Understanding Accidental Activation

Intent

This section contains the main explanatory content of the Understanding. It explains why the Guideline or Success Criterion exists and, at a high level, how to meet it.

People with various disabilities can inadvertently initiate touch or mouse events with unwanted results. Up-Event activation refers to the activation of a component when the trigger stimulus is released. For example, for touchscreen interaction the event would be triggered when a finger is lifted from the touchscreen at the end of a tap.There is a distinction between when someone touches a screen and when they remove their finger. On a mouse there is a difference between mouse down (initiating a click) and mouse up (releasing the finger). Authors can reduce the problem of users inadvertently triggering an action, by making activation on the up-event. This gives users the opportunity to move their finger or other pointer (e.g. mouse) away from the wrong target once they hit it. If touch down activation is necessary, there are several options:

A confirmation alert allows the user to change their mind
An undo button or other mechanism allows the user to reverse the action.
A setting in preferences allows the user to choose whether activation happens on the down or up event.

Generic platform activation/click events generally trigger on up and when they do, they are also allowed. For example, in the case of mouse interactions, the "click" event in JavaScript triggers on release of the primary mouse button, and is an example of an implicit up-event.

Examples of where timing of the activation is essential would be:

An activity that would be invalid if activation waited for the up-event such as a piano program.
A program for shooting skeets where waiting for the "up" event would invalidate the activation.

Long press activation and 3D touch can be used as long as one of the above listed alternatives is present, and there is another conforming way to provide the action performed by the control.

Benefits

This explains how following the success criterion benefits particular types of users with disabilities.

Makes it easier for all users to recover from hitting the wrong target.
Helps people with visual disabilities, cognitive limitations, and motor impairments by reducing the chance that a control will be accidentally activated or action will occur unexpectedly.
Individuals who are unable to detect changes of context are less likely to become disoriented while navigating a site

Examples

Examples in Understanding pages are normally simple lists of hand-waving examples. Sometimes, examples are instead provided in sub-sections with headings. In either case, examples should stay high-level and not get into code specifics, which is for techniques.

For interface elements that have a single tap or long press as input, the corresponding event is triggered when the finger is lifted inside that element.
A phone dialling application has number keys that are activated on touch down. A user can undo an unwanted number by hitting the backspace button to delete a mistaken digit.

Example

Techniques

This section references techniques that can be used to meet the Guideline or Success Criterion. There are sub-sections for sufficient techniques, advisory techniques, and failures.

Within each sub-section, there may be "situations" to describe when a set of techniques need to be considered. Remove the sub-section and heading if situations are not used.
Techniques are provided in an unordered list. Reference techniques by linking to the filename of the technique and using the technique ID as link text. Use unlinked plain text if the technique has not been written yet.
If more than one technique must be used for full sufficiency, list them in the same bullet separated by "AND".
If a general technique requires technology-specific techniques to be implemented, end the bullet with "using" and provide a sub-list of those techniques.
Square brackets indicate optional components.

Remove any parts of the template that are not used, such as the section and heading for situations, sub-lists of techniques, or the "AND" construction. Also remove the square brackets around placeholder optional components.

Sufficient

Techniques that are sufficient to meet the Guideline or Success Criterion.

Situation

Activating a control using the up-Event in HTML, iOS and Android
M029(wiki) Touch events are only triggered when touch is removed from a control
FM001 Failure of SC 2.5.3 due to activating a button on initial touch location rather than the final touch location

Advisory

Techniques that are not sufficient by themselves to meet the Guideline or Success Criterion.

Same template as sufficient techniques.

Failure

Techniques that document conditions that would cause the page not to meet the Guideline or Success Criterion, even if sufficient techniques are also used.