presentation constant

An element whose implicit native role semantics will not be mapped to the accessibility API.

The intended use is when an element is used to change the look of the page but does not have all the functional, interactive, or structural relevance implied by the element type, or may be used to provide for an accessible fallback in older browsers that do not support WAI-ARIA.

Example use cases:

An element whose content is completely presentational (like a spacer image, decorative graphic, or clearing element); An image that is in a container with the img role and where the full text alternative is available and is marked up with aria-labelledby and (if needed) aria-describedby;An element used as an additional markup 'hook' for CSS; orA layout table and/or any of its associated rows, cells, etc. For any element with a role of presentation and which is not focusable, the user agent MUST NOT expose the implicit native semantics of the element (the role and its states and properties) to accessibility APIs. However, the user agent MUST expose content and descendant elements that do not have an explicit or inherited role of presentation. Thus, the presentation role causes a given element to be treated as having no role or to be removed from the accessibility tree, but does not cause the content contained within the element to be removed from the accessibility tree.

The presentation role is used on an element that has implicit native semantics, meaning that there is a default accessibility API role for the element. Some elements are only complete when additional descendant elements are provided. For example, in HTML, table elements (matching the grid role) require tr descendants (the row role), which in turn require th or td children (the gridcell, columnheader, rowheader roles). Similarly, lists require list item children. The descendant elements that complete the semantics of an element are described in WAI-ARIA as required owned elements.

When an explicit or inherited role of presentation is applied to an element with the implicit semantic of a WAI-ARIA role that has required owned elements, in addition to the element with the explicit role of presentation, the user agent MUST apply an inherited role of presentation to any owned elements that do not have an explicit role defined. Also, when an explicit or inherited role of presentation is applied to a host language element which has required children as defined by the host language specification, in addition to the element with the explicit role of presentation, the user agent MUST apply an inherited role of presentation to any required children that do not have an explicit role defined. For any element with an explicit or inherited role of presentation and which is not focusable, user agents MUST ignore role-specific WAI-ARIA states and properties for that element. For example, in HTML, a ul or ol element with a role of presentation will have the implicit native semantics of its li elements removed because the list role to which the ul or ol corresponds has a required owned element of listitem. Likewise, although an HTML table element does not have an implicit native semantic role corresponding directly to a WAI-ARIA role, the implicit native semantics of its thead/tbody/tfoot/tr/th/td descendants will also be removed, because the HTML specification indicates that these are required structural descendants of the table element. Explicit roles on a descendant or owned element override the inherited role of presentation, and cause the owned element to behave as any other element with an explicit role. If the action of exposing the implicit role causes the accessibility tree to be malformed, the expected results are undefined and the user agent MAY resort to an internal recovery mechanism to repair the accessibility tree.

Note: Only the implicit native semantics of elements that correspond to WAI-ARIA required owned elements are removed. All other content remains intact, including nested tables or lists, unless those elements also have a explicit role of presentation applied.

For any element with an explicit or inherited role of presentation, user agents MUST apply an inherited role of presentation to all host-language-specific labeling elements for the presentational element. For example, a table element with a role of presentation will have the implicit native semantics of its caption element removed, because the caption is merely a label for the presentational table.

For any element with an explicit or inherited role of presentation, user agents MUST ignore any non-global, role-specific WAI-ARIA states and properties. However, the user agent MUST always expose global WAI-ARIA states and properties to accessibility APIs, even if an element has an explicit or inherited role of presentation.

See: developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/presentation_role

Implementation

Role class