For functionality that can be operated using a single pointer, at least one of the following is true:
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;
The up-event reverses any outcome of the preceding down-event;
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).
The intention of 2.5.2: Pointer Cancellation is to ensure accidental pointers of the user gestures do not lead to delete or undo a control or action. The specific intention is to provide a direction for the content authors in implementing pointer cancellation features.
The two events that help in canceling or aborting an action can be on press of a control or on release of the action on a control. These are pointer / gestured based. The equivalent mouse interactions are click and release of mouse pointers. In this success criterion 2.5.2: Pointer Cancellation, the press, click or pointer touch are the down events and release of touch pointer or mouse pointer is up event.
Cancellation with up event
This success criterion 2.5.2: Pointer Cancellation recommends to use up event for to cancel or abort an action. If the user accidentally touches or press on a control they can move the pointer away from the control before releasing the pointer (up event). By moving away from the control they are effectively avoiding from initiating the action on the control. User gets a visual feedback when the pointer is pressed (down event), if they observe that they pressed a wrong control its easy to terminate the action only if the up event initiates the action.
If the touch or press on a control is accurate then the user can release the pointer within the boundaries of the target control. On releasing the pointer or lifting the pointer gesture (up event) within the target of the control will activate it. This means the up event is the preferred way of either activating or canceling a pointer action.
The click event fundamentally understood as mouse click which is equivalent to the down event. Practically mouse click on any control does not initiate an action. The action is initiated only when the user releases the mouse pointer. The click event work as press on a touch context and a key press for a keyboard.
Drag and Drop
The up event is appropriate even for complex interactions such as drag and drop. The down event / press / click will initiate the grab of the draggable control. With the visual feedback or by other means if the user finds that the grabbed control is not the right control, they can move back the pointer to the initial position and initiates the up event. This will abort dragging the unwanted action. If the right control is picked, then the user will fire the up event at the target location. This process will accurately complete the drop action on the intended location.
Down event initiates an action on a control but is not effective to complete the action in most case as discussed earlier. However, some specific situations make it easy for completing the action with down event. For example the keyboard emulation. The typing becomes quick and easy if the action happens on down event. Most keyboards have back space or delete buttons to cancel if a wrong action is initiated with the down event. Typing a letter on up event on a touch screen keyboard is an unexpected behavior. As down event fires the action of typing the letters, an effective way of undo will be beneficial though it is not essential as the back space or delete keys can cancel the action.
The voiceover IOS touch typing and direct touch typing will effectively explain the use of onscreen keyboard with up event and down event. Read the article 5 ways of typing with voiceover for experiencing the same.
Benefits of 2.5.2 Pointer Cancellation
- 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 an action will occur unexpectedly, and also ensures that where complex controls are activated, a means of Undoing or Aborting the action is available.
- Individuals who are unable to detect changes of context are less likely to become disoriented while navigating a site.
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