aria-activedescendant is used to manage focus within a composite widget.
The element with the attribute aria-activedescendant retains the active document
focus; it indicates which of its child elements has secondary focus by assigning
the ID of that element to the value of aria-activedescendant. This pattern is
used to build a widget like a search typeahead select list. The search input box
retains document focus so that the user can type in the input. If the down arrow
key is pressed and a search suggestion is highlighted, the ID of the suggestion
element will be applied as the value of aria-activedescendant on the input
element.
Because an element with aria-activedescendant must be tabbable, it must either
have an inherent tabIndex of zero or declare a tabIndex of zero with the tabIndex
attribute.
This rule takes no arguments.
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