aria-setsize

Browsers automatically calculate the set size and position for each item in a group of items, like the number of <li>s in a list, buttons in a same-named group of radio buttons, and <option>s in a <select>. Assistive technologies, like screen readers, take advantage of this state management to report set sizes to the user.

When the DOM is not complete, the browser calculation of the number of items in a set can be incorrect. When only a subset of items, such as list items, are loaded into the DOM, the browser calculates the number of items based only on those present. The aria-setsize attribute should be used to override the browser's incorrect count. It defines the number of items in the current set of listitems or treeitems had the entire set been loaded.

aria-setsize attribute is set on each item, rather than on any containing element. The value is the same for each item: an integer reflecting number of items in the complete set, or -1 if the set size is unknown. If all the items are present in the DOM, the browser can calculate the set size and the position of each item, making both aria-setsize and aria-posinset unnecessary.

Elements with the aria-setsize generally have the aria-posinset attribute included as well to indicate the position of that item within the set. The aria-posinset value is between 1 and the positive value of aria-setsize.

For example, in a page's comments section, When comments in are not all in the DOM, such as when comments are paginated, the level, total number of comments, and position of each comment should be set with ARIA. The hierarchical level of comments can be indicated with aria-level. Group positional information is indicated with aria-posinset and aria-setsize.

When a feed has a static number of articles, aria-setsize can be added to each article element with the value being either the total number of articles loaded or the total number in the feed. The value chosen depends on which value is most helpful to users. If the number of articles is extremely large, indefinite, or changes often, aria-setsize="-1" can be set to communicate the size of the set is unknown.

In a listbox, when the complete set of available options is not present in the DOM due to dynamic loading on scroll, both aria-setsize and aria-posinset can be set on each option.

In a tree view, if the complete set of available nodes is not present in the DOM due to dynamic loading as the user moves focus in or scrolls the tree, each node has aria-level, aria-setsize, and aria-posinset set.

In a menu, aria-setsize is set on all menuitem, menuitemcheckbox, or menuitemradio roles, with the value being the total number of items in the menu, excluding any separators.

The following example shows items 5 through 8 in a set of 16.

<h2 id="label_fruit">Available Fruit</h2>
<ul role="listbox" aria-labelledby="label_fruit">
  <li role="option" aria-setsize="16" aria-posinset="5">apples</li>
  <li role="option" aria-setsize="16" aria-posinset="6">bananas</li>
  <li role="option" aria-setsize="16" aria-posinset="7">cantaloupes</li>
  <li role="option" aria-setsize="16" aria-posinset="8">dates</li>
</ul>

To orient the user, assistive technologies would list the bananas above as "item 6 out of 16."

<integer>

The number of items in the full set or -1 is the set size is unknown.

Element.ariaSetSize

The ariaSetSize property, part of the Element interface, reflects the value of the aria-setsize attribute.

ElementInternals.ariaSetSize

The ariaSetSize property, part of the ElementInternals interface, reflects the value of the aria-setsize attribute.

Used in roles:

• article
• associationlistitemkey
• associationlistitemvalue
• comment
• listitem
• menuitem
• option
• radio
• row
• tab

Inherits into roles:

• comment
• menuitemcheckbox
• menuitemradio
• treeitem

• aria-posinset
• W3C WAI-ARIA practices:
  • Treegrid Email Inbox example
  • Navigation Treeview example
  • File Directory Treeview Example Using Declared Properties