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Using WAI-ARIA state and property attributes to expose the state of a user interface component

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Status

Applicability

This technique applies to technologies that support WAI-ARIA, such as HTML.

WCAG references

User Agent and Assistive Technology Support Notes

Description

The objective of this technique is to use WAI-ARIA state and property attributes to expose the state, properties and values of a user interface component so that they can be read and set by assistive technology, and so that assistive technology is notified of changes to these values. The WAI-ARIA specification provides a normative description of each attribute, and the role of the user interface elements that they support. When rich internet applications define new user interface widgets, exposing the state and property attributes enables users to understand the widget and how to interact with it.

Examples

Example 1: A toggle button

A widget with role button acts as a toggle button when it implements the attribute aria-pressed. When aria-pressed is true, the button is in a "pressed" state. When aria-pressed is false, it is not pressed. If the attribute is not present, the button is a simple command button.

The following snippet from The Open Ajax Accessibility Examples, Example 38, shows WAI-ARIA mark-up for a toggle button that selects bold text:

  <li id="bold1"  
    class="toggleButton"
    role="button"
    tabindex="0"
    aria-pressed="false"
    aria-labelledby="bold_label"
    aria-controls="text1"
      ><img src="http://www.oaa-accessibility.org/media/examples/images/button-bold.png" alt="bold text" align="middle"></li>

The li element has a role of "button" and an "aria-pressed" attribute. The following excerpt from the Javascript for this example updates the value of the "aria-pressed" attribute:

  /**
   * togglePressed() toggles the aria-pressed atribute between true or false
   *
   * @param ( id object) button to be operated on
   *
   * @return N/A
   */
  function togglePressed(id) {
  
    // reverse the aria-pressed state
    if ($(id).attr('aria-pressed') == 'true') {
      $(id).attr('aria-pressed', 'false');
    }
    else {
      $(id).attr('aria-pressed', 'true');
    }
  }

This button is available as part of the working example of Example 38 - Toolbar using inline images for visual state, on the OpenAjax Alliance site.

Example 2: A slider

A widget with role slider lets a user select a value from within a given range. The slider represents the current value and the range of possible values via the size of the slider and the position of the handle. These properties of the slider are represented by the attributes aria-valuemin, aria-valuemax, and aria-valuenow.

The following snippet from The Open Ajax Accessibility Examples, Example 32, shows WAI-ARIA mark-up for a slider created in Javascript. Note that the javascript sets the attributes aria-valuemin, aria-valuemax, and aria-valuenow:

   var handle = '<img id="' + id + '" class="' + (this.vert == true ? 'v':'h') +'sliderHandle" ' +
    'src="http://www.oaa-accessibility.org/media/examples/images/slider_' + (this.vert == true ? 'v':'h') + '.png" ' + 'role="slider" ' +
    'aria-valuemin="' + this.min +
    '" aria-valuemax="' + this.max +
    '" aria-valuenow="' + (val == undefined ? this.min : val) +
           '" aria-labelledby="' + label +
           '" aria-controls="' + controls + '" tabindex="0"></img>';

The following excerpt from the Javascript for this example updates the value of the "aria-valuenow" attribute when the value of the slider handle is changed:

 slider.prototype.positionHandle = function($handle, val) {
    ...
   // Set the aria-valuenow position of the handle
  $handle.attr('aria-valuenow', val);
   ...
  }

This slider is available as part of the working example of Example 32 - Slider, on the OpenAjax Alliance site.

Resources

Related Techniques

Tests

Procedure

The WAI-ARIA specification, Section 5.3, Categorization of Roles defines the required and inherited states and properties for each role.

For a user interface component using the WAI-ARIA role attribute:

  1. Check that the required states and properties for the role are present.
  2. Check that no WAI-ARIA states or properties that are neither required, supported, nor inherited are present.
  3. Check that the state and property values are updated to reflect the current state when the user interface component changes state.

Expected Results

  • #1, #2 and #3 are true