RE: use of aria-hidden to provide a text description not visible on the page.

I believe the intent of aria-hidden was to hide information that IS presented visually from the accessibility API.  For example an image that is used to indicate the state of a tree leaf does not need to be part of the accessibility tree if aria-expanded state is being used.

This way any aria- enabled technology would ignore the ALT text of the image, and assistive technology that is not ARIA aware could may use the ALT content of the image to describe state.

Jon

Jon Gunderson, Ph.D.
Coordinator Information Technology Accessibility
Disability Resources and Educational Services

Rehabilitation Education Center
Room 86
1207 S. Oak Street
Champaign, Illinois 61820

Voice: (217) 244-5870

WWW: http://www.cita.illinois.edu/

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From: wai-xtech-request@w3.org [mailto:wai-xtech-request@w3.org] On Behalf Of James Craig
Sent: Tuesday, September 14, 2010 4:02 PM
To: sailesh.panchang@deque.com
Cc: 'Steven Faulkner'; 'David Bolter'; 'Leif Halvard Silli'; 'Andi Snow-Weaver'; 'W3C WAI-XTECH'; 'HTML Accessibility Task Force'
Subject: Re: use of aria-hidden to provide a text description not visible on the page.

On Sep 14, 2010, at 1:40 PM, Sailesh Panchang wrote:


I have been reading this and thinking why should one use this attribute when CSS properties display:none and other properties to place content offscreen are well supported by browsers and  AT.
Secondly, hiding and revealing is a presentational function which is best done by CSS. Using an ARIA attribute to do this  in the HTML code is like  using  a font / color attribute in HTML, is it not?

Not at all. All of the ARIA attributes have semantic meanings. Please see the spec for what those meanings are, as well as why one should use them. If, after reading the relevant portion of the spec, it's not clear when or why to use something, please send a comment or clarification request to public-pfwg-comments@w3.org<mailto:public-pfwg-comments@w3.org>. Relevant portion of the spec follows.

Cheers,
James

http://www.w3.org/WAI/PF/aria/complete#aria-hidden
aria-hidden (state)

Indicates that the element<http://www.w3.org/WAI/PF/aria/complete#def_element> is not visible or perceivable<http://www.w3.org/WAI/PF/aria/complete#def_perceivable> to any user as implemented by the author. Also see aria-disabled<http://www.w3.org/WAI/PF/aria/complete#aria-disabled>.

If an element is only visible after some user action, authors MUST set the aria-hidden attribute<http://www.w3.org/WAI/PF/aria/complete#def_attribute> to true. When the element is presented, authors MUSTset the aria-hidden attribute to false or remove the attribute, indicating that the element is visible. Some assistive technologies access WAI-ARIAinformation directly through the DOM and not through platform accessibility supported by the browser. Authors MUST set aria-hidden="true" on content that is not displayed, regardless of the mechanism used to hide it. This allows assistive technologies<http://www.w3.org/WAI/PF/aria/complete#def_at> or user agents<http://www.w3.org/WAI/PF/aria/complete#def_useragent> to properly skip hidden<http://www.w3.org/WAI/PF/aria/complete#def_hidden> elements in the document.

It is recommended that authors key visibility of elements off this attribute, rather than change visibility and separately have to remember to update thisproperty<http://www.w3.org/WAI/PF/aria/complete#def_property>. CSS 2 provides a way to select on attribute values<http://www.w3.org/TR/1998/REC-CSS2-19980512/selector.html#q10> ([CSS<http://www.w3.org/WAI/PF/aria/complete#ref_CSS>]). The following CSS declaration makes content visible unless the aria-hiddenattribute is true; scripts need only update the value<http://www.w3.org/WAI/PF/aria/complete#def_value> of this attribute to change visibility:

[aria-hidden="true"] { visibility: hidden; }

Note: At the time of this writing, this CSS example, while technically correct, will not redraw styles properly in some browsers if the attribute's value is changed dynamically. It may be necessary to toggle a class name, or otherwise force the browser to redraw the styles properly.

Note: Authors are reminded that visibility:hidden<http://www.w3.org/TR/CSS21/visufx.html#visibility> and display:none<http://www.w3.org/TR/CSS21/visuren.html#propdef-display> apply to all CSS media types<http://www.w3.org/TR/CSS21/media.html#media-types>; therefore, use of either will hide the content from assistive technologies that access the DOM through a rendering engine. However, in order to support assistive technologies that access the DOM directly, or other authoring techniques to visibly hide content (for example, opacity or off-screen positioning<http://www.w3.org/TR/CSS21/visuren.html#propdef-position>), authors need to ensure the aria-hidden attribute is always updated accordingly when an element is shown or hidden.

Authors MAY, with caution, use aria-hidden to hide visibly rendered content from assistive technologies only if the act of hiding this content is intended to improve the experience for users of assistive technologies by reducing redundancy. Authors using aria-hidden to hide visible content from screen readers MUST ensure that identical or equivalent meaning and functionality is exposed to assistive technologies.

Note: Authors are advised to use extreme caution and consider a wide range of disabilities when hiding visibly rendered content from assistive technologies. For example, a sighted, dexterity-impaired individual may use voice-controlled assistive technologies to access a visual interface. If an author hides visible link text "Go to checkout" and exposes similar, yet non-identical link text "Check out now" to the accessibility API, the user may be unable to access the interface they perceive using voice control. Similar problems may also arise for screen reader users. For example, a sighted telephone support technician may attempt to have the blind screen reader user click the "Go to checkout" link, which they may be unable to find using a type-ahead item search ("Go to...").
Characteristics of aria-hidden

Characteristic

Value

Used in Roles:

All elements of the base markup

Value:

true/false<http://www.w3.org/WAI/PF/aria/complete#valuetype_true-false>


Values of aria-hidden

Value

Description

true:

Indicates that this section of the document and its children are hidden from the rendered view.

false (default):

Indicates that this section of the document is rendered.

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