Radio Group Example Using aria-activedescendant

This example implements the features of the Radio Group Design Pattern for two radio groups -- one for choosing a pizza crust and another for choosing a delivery method. This implementation uses aria-activedescendant for informing assistive technologies which radio button has visual focus.

Similar examples include:

Radio Group Example Using Roving tabindex: A radio button group that uses roving tabindex for managing keyboard focus.

Example

Pizza Crust

Regular crust
Deep dish
Thin crust

Pizza Delivery

Pick up
Home Delivery
Dine in Restaurant

Accessibility Features

Uses CSS attribute selectors for synchronizing aria-checked state with the visual state indicator.
Uses CSS :hover and :focus pseudo-selectors for styling visual keyboard focus and hover.
- Focus indicator encompasses both radio button and label, making it easier to perceive which option is being chosen.
- Hover changes background of both radio button and label, making it easier to perceive that clicking either the label or button will activate the radio button.

Keyboard Support

NOTE: When visual focus is on a radio button in the radio group, DOM focus remains on the radio group container and the value of aria-activedescendant on the radio group refers to the radio button that is visually indicated as focused. Where the following descriptions of keyboard commands mention focus, they are referring to the visual focus indicator, not DOM focus. For more information about this focus management technique, see Using aria-activedescendant to Manage Focus.

Key	Function
`Tab`	Moves focus to the checked `radio` button in the `radiogroup`. If a `radio` button is not checked, focus moves to the first `radio` button in the group.
`Space`	If the `radio` button with focus is not checked, changes the state to `checked`. Otherwise, does nothing. Note: The state where a radio is not checked only occurs on page load.
`Right arrow`	Moves focus to and checks the next `radio` button in the group. If focus is on the last `radio` button, moves focus to the first `radio` button. The state of the previously checked radio button is changed to unchecked.
`Down arrow`	Moves focus to and checks the next `radio` button in the group. If focus is on the last `radio` button, moves focus to the first `radio` button. The state of the previously checked radio button is changed to unchecked.
`Left arrow`	Moves focus to and checks the previous `radio` button in the group. If focus is on the first `radio` button, moves focus to and checks the last `radio` button. The state of the previously checked radio button is changed to unchecked.
`Up arrow`	Moves focus to and checks the previous `radio` button in the group. If focus is on the first `radio` button, moves focus to and checks the last `radio` button. The state of the previously checked radio button is changed to unchecked.

Role, Property, State, and Tabindex Attributes

Role	Attributes	Element	Usage
`radiogroup`		`ul`	Identifies the element as a container for a group of `radio` buttons.
	`aria-labelledby="[IDREF]"`	`ul`	Refers to the element that contains the label of the radio group.
	`tabindex="0"`	`ul`	Includes the radio group in the page `Tab` sequence. Applied to the radio group because `aria--activedescendant` is used to manage focus as described below.
	`aria-activedescendant="[IDREF]"`	`ul`	When a radio button in the radio group is visually indicated as having keyboard focus, refers to that radio button. When arrow keys are pressed, the JavaScript changes the value. Enables assistive technologies to know which element the application regards as focused while DOM focus remains on the radio group element. For more information about this focus management technique, see Using aria-activedescendant to Manage Focus.
`radio`		`li`	Identifies the element as an ARIA `radio` button. The accessible name is computed from the child text content of the element.
	`aria-checked="false"`	`li`	Identifies `radio` buttons which are not checked. CSS attribute selectors (e.g. `[aria-checked="false"]`) are used to synchronize the visual states with the value of the `aria-checked` attribute. The CSS `::before` pseudo-class is used to indicate visual state of unchecked radio buttons to support high contrast settings in operating systems and browsers.
	`aria-checked="true"`	`li`	Identifies the `radio` button which is checked. CSS attribute selectors (e.g. `[aria-checked="true"]`) are used to synchronize the visual states with the value of the `aria-checked` attribute. The CSS `::before` pseudo-class is used to indicate visual state of checked radio buttons to support high contrast settings in operating systems and browsers.

Javascript and CSS Source Code

CSS: radio.css
Javascript: radioGroupActiveDescendant.js
Javascript: radioButtonActiveDescendant.js