Defines the number of items in the current set of listitems or treeitems. Not required if all elements in the set are present in the DOM.
Description

Defines the number of items in the current set of listitems or treeitems. Not required if all elements in the set are present in the DOM. See related aria-posinset.

This property is marked on the members of a set, not the container element that collects the members of the set. To orient the user by saying an element is "item X out of Y," the assistive technologies would use X equal to the aria-posinset attribute and Y equal to the aria-setsize attribute.

If all items in a set are present in the document structure, it is not necessary to set this property, as the user agent can automatically calculate the set size and position for each item. However, if only a portion of the set is present in the document structure at a given moment (in order to reduce document size), this property is needed to provide an explicit indication of set size.

Authors MUST set the value of aria-setsize to an integer equal to the number of items in the set. If the total number of items is unknown, authors SHOULD set the value of aria-setsize to -1.

When exposing aria-setsize on a menuitem, menuitemcheckbox, or menuitemradio, authors SHOULD set the value of aria-setsize based on the total number of items in the menu, excluding any separators.

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ARIA