Przeciąganie
Objaśnienie
KS
2.5.7
Status
This understanding document is part of the draft WCAG 2.2 content. It may change or be removed before the final WCAG 2.2 is published.
Dragging Movements
AA
All functionality that uses a dragging movement for operation can be achieved by a single pointer without dragging, unless dragging is essential or the functionality is determined by the user agent and not modified by the author.
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).
Is there an assistive technology that helps people with mobility impairments? The group would like feedback on the frontier between AT & author responsibility.
Intent of Dragging Movements
The intent of this Success Criterion is to ensure functionality that uses a dragging movement (e.g., sliders, drag-and-drop interfaces) has another single pointer mode of operation without the need for the dexterity required to drag elements.
Some people cannot perform dragging movements in a precise manner. Others use a specialized or adapted input device, such as a trackball, head pointer, eye-gaze system, or speech-controlled mouse emulator, which may make dragging cumbersome and error-prone.
When an interface implements functionality that uses dragging movements, users perform four discrete actions:
- tap or click to establish a starting point, then
- press and hold that contact while...
- performing a repositioning of the pointer, before...
- releasing the pointer at the end point.
Not all users can accurately press and hold that contact while also repositioning the pointer. An alternative method must be provided so that users with mobility impairments who use a pointer (mouse, pen, or touch contact) can use the functionality.
This requirement is separate from keyboard accessibility because people using a touch screen device may not use a physical keyboard. Keyboard specific interactions such as tabbing or arrow keys may not be possible when encountering a drag and drop control. Note, however, that providing a text input can be an acceptable single-pointer alternative to dragging. For example, an input beside a slider could allow any user to enter a precise value for the slider. In such a situation, the on-screen keyboard that appears for touch users offers a single-pointer means of entering an alphanumeric value.
Relationship to other requirements
Success Criteria 2.1.1 Keyboard and 2.1.3 Keyboard (No Exception) require dragging features to be keyboard accessible. However, achieving keyboard equivalence for a dragging operation does not automatically meet this Success Criterion. It is possible to create an interface that works with dragging and keyboard controls that does not work using only clicks or taps. While many designs can be created for a dragging alternative which address both keyboard accessibility and operability by single pointer operation, the two requirements should be assessed independently.
This Success Criterion applies to dragging movements as opposed to pointer gestures, which are covered in Success Criterion 2.5.1 Pointer Gestures. Pointer gestures include directional path-based as well as multi-point gestures. In contrast, for dragging movements, only the start and end point of the movement matters, not the actual path.
Additional examples are selection rectangles that set the first x/y rectangle coordinate at the pointer position via a pointer down-event, and the second x/y coordinate, after a dragging movement, at the next up-event. A similar example is a connecting line drawn between two different items on the screen, as in an allocation test where users are required to draw a line between questions and corresponding answers. In these cases, the dragging movement requires an alternative way to accomplish the same action that does not rely on the dragging movement. For example, two separate single tap or click actions may define the rectangle coordinates or the start and end points of a connecting line.
Alternatives for dragging movements on the same page
Where functionality can be executed via dragging movements and an equivalent option exists that allows for single-pointer access without dragging, this Success Criterion is passed. It does not have to be the same component, so long as the functionality is equivalent. An example is a color wheel where a color can be changed by dragging an indicator. In addition, text fields for the numerical input of color values allow the definition of a color without requiring dragging movements. (Note that a text input is considered device agnostic; although the purpose is to enter characters, text entry can take place through voice, pointer or keyboard.)
Distinguishing dragging movements from path-based pointer gestures
Dragging movements covered in this Success Criterion are pointer interactions where only the start- and endpoints matter. Once the pointer engages with a target, the direction of the dragging movement does not factor into the interaction until the pointer disengages the target. Since the dragging movement does not have an intermediate point, the dragging movement can go in any direction. Path-based gestures are covered in Success Criterion 2.5.1 Pointer Gestures. For more details, refer to Understanding Success Criterion 2.5.1 Pointer Gestures
Benefits of Dragging Movements
- Users who struggle with performing dragging movements can still operate an interface with a pointer interface.
Examples of Dragging Movements with alternatives
- A map allows users to drag the view of the map around, and the map has up/down/left/right buttons to move the view as well.
- A sortable list of elements may, after tapping or clicking on a list element, provide adjacent controls for moving the element up or down in the list by simply tapping or clicking on those controls.
- A kanban implementation may provide an additional pop-up menu after tapping or clicking on elements for moving the selected element to another kanban silo by tapping or clicking on pop-up menu entries.
- A radial control widget (color wheel) where the value can be set by dragging the marker for the currently selected color to another position, also allows picking another color value by tapping or clicking on another place in the color wheel.
- A linear slider control widget, where the value can be set by dragging the visual indicator (thumb) showing the current value, allows tapping or clicking on any point of the slider track to change the value and set the thumb to that position.