A button that expands to reveal a listbox in a flyout.
Avoid calling a listbox button a "dropdown"! The term "dropdown" is ambiguous and could be confused with a menu button, combobox, select or any other kind of overlay that "drops down".
Updated: March 15th, 2021 (labelling)
widget: the pattern as a whole, comprised of the parts below
button: the button that opens the flyout
flyout: the overlay that contains the listbox
listbox: the list of options
option: an option, with state
label: internal and/or external text element(s)
A listbox button's accessible label must at all times reflect its function.
Care is needed when labelling a listbox button! A listbox button attempts to mimic the behaviour of an HTML select by displaying the currently selected value in its collapsed state. In HTML however, a button is labelled by its inner text, whereas a select is labelled by an external label tag.
All of this leaves us with a conundrum, with three potential solutions outlined below.
We can use
aria-labelledbyto stitch together an external text element with the internal value, this creating a compound label.
<span id="el1">Colour</span><button aria-labelledby="el1 el2"><span id="el2">blue</span></button>
The button's inner text can be written as a key/value pair, where key denotes purpose and value represents the currently selected option.
We can write our option values such that the context can always be derived from the option value text alone (this isn't always easy or recommended).
<div role="option">Colour blue</div>
This section provides interaction design for keyboard, screen reader & pointing devices.
With focus on button, pressing
SPACEBARwill will toggle the expanded state of button. On expand, keyboard focus should move to the listbox. The listbox implements an active-descendant keyboard model.
With focus on listbox,
ARROW KEYSwill navigate the options,
ESCAPEkey will collapse listbox and move focus on to button.
TABkey will collapse listbox and move focus to next interactive page element.
SHIFT-TABwill move focus back to button and listbox will remain expanded.
With virtual cursor on button, screen reader should announce role, label (see "Best Practices" section above), value & state..
Clicking or tapping button will toggle expanded state of flyout.
Clicking or tapping an option in flyout will update button value and collapse the flyout.
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