After months of long discussions the IAccessible2 group released 1.3 version. It was probably most disputable release after the initial shipping. A number of assistive technology vendors requested a number of changes for better integration with the browser. So it took a time to find a common multiplier for all ideas.
So updated IAccessible2 API require some engineering love and thus it will be implemented in Firefox by parts. It'd be helpful to know which features are most crucial and needed for you as AT developer so we can give them a priority. To let us know please leave a comment in the bug or just ping me saying that. Alternatively you can vote for or comment right into the interesting bug (see sections below).
IA2_ROLE_COMPLEMENTARY_CONTENT is supposed for HTML5 aside element and WAI ARIA complementray role (see Mozilla bug).
A new IA2_STATE_PINNED state will be exposed on pinned tabs in Firefox UI (see Mozilla bug).
Technically speaking IA2_STATE_CHECKABLE was introduced in place of hacks used to workaround a lack of this state. For example Firefox exposes checkable object attribute (IAccessible2 hack) and STATE_SYSTEM_MARQUEED (pure MSAA approach). See Mozilla bug.
There is a bunch of new relations introduced to simplify a navigation through the hierarchy. Now you can quickly move to
Also now you can get a next and previous elements in tab order (IA2_RELATION_NEXT_TABBABLE and IA2_RELATION_PREVIOUS_TABBABLE). It's useful for AT that implement own in-page navigation (see Mozilla bug).
New IA2_RELATION_NODE_PARENT_OF is a dual relation to IA2_RELATION_NODE_CHILD_OF. It's useful to get all logical children of the accessible (as you know a logical parent-child relation may be different from parent-child relation defined by accessible tree). Example is aria-owns (like aria-owns tree) and flat structured hierarchies like XUL tree (used for message list in Thunderbird) or ARIA tree where the hierarchy is supplied by aria-level like:
<ul role="tree">
<li role="treeitem" aria-level="1">Item 1</li>
<li role="treeitem" aria-level="2">Item 1.1</li>
</ul>
See Mozilla bug.
IAccessibleDocument is a new interface that allows you to get an anchor target, i.e. an element that the page was scrolled to after the page was loaded. Also an object of this interface is returned by relations like IA2_RELATION_CONTAINING_DOCUMENT and IA2_RELATION_CONTAINING_WINDOW. See Mozilla bug.
The idea was to manage the media content by accessible actions (IA2 group got parsimonious for a new interface so the existing mechanism was reused).
If a screen reader starts, say, a subtitled video then it invokes IA2_ACTION_OPEN action. The browsers plays a portion of subtitled video and stops it until a screen reader invokes IA2_ACTION_COMPLETE action. This action is used to notify the browser that screen reader consumed the portion of played video subtitles, for example, it finished reading of them. If screen reader is no longer interesting to manage the media playback then it invokes IA2_ACTION_CLOSE action.
If more than one AT tries to manage the same media (i.e. AT that invoked 'open' action) then the browser holds on the video playback until all AT invoke 'complete' action. See Mozilla bug.
After IAccessible2 implementation by Firefox and AT it got clear that IAccessible2 API can be improved in certain ways to make the intercommunication between the browser and AT faster. So number of changes was introduced for performance matter.
Now you can obtain object attributes by name rather than get them all together and then parse the string (see Mozilla bug).
Now you have a method to get relation targets by type. You don't need to get all relations when you need a single one (see Mozilla bug).
You have a fast way to get a text accessible containing a caret in the subtree and the caret offset in the text accessible. Previously the algorithm to find an accessible containing the caret failed on some cases. The idea of that approach was that a screen reader should crawl down the hierarchy asking for caret position until it reaches a deepest text accessible having the caret. It failed if you meet non text accessible on the way. As a workaround the screen readers navigated children. While the workaround worked well but it was really slow (see Mozilla bug).
The change is similar to object attributes. A light alternative to the method used to get all text attributes was added. Now you can specify a string filter and get attributes you need (see Mozilla bug).
Usually AT needs all hyperlinks at once. Getting them one by one is unperformant (especially for out of process AT) and requires a cache implementation on the browser side. So a new method to get all hyperlinks has been introduced (see Mozilla bug).
So updated IAccessible2 API require some engineering love and thus it will be implemented in Firefox by parts. It'd be helpful to know which features are most crucial and needed for you as AT developer so we can give them a priority. To let us know please leave a comment in the bug or just ping me saying that. Alternatively you can vote for or comment right into the interesting bug (see sections below).
Roles
IA2_ROLE_COMPLEMENTARY_CONTENT is supposed for HTML5 aside element and WAI ARIA complementray role (see Mozilla bug).
States
A new IA2_STATE_PINNED state will be exposed on pinned tabs in Firefox UI (see Mozilla bug).
Technically speaking IA2_STATE_CHECKABLE was introduced in place of hacks used to workaround a lack of this state. For example Firefox exposes checkable object attribute (IAccessible2 hack) and STATE_SYSTEM_MARQUEED (pure MSAA approach). See Mozilla bug.
Relations
There is a bunch of new relations introduced to simplify a navigation through the hierarchy. Now you can quickly move to
- nearest containing document, instance of IAccessibleDocument (IA2_RELATION_CONTAINING_DOCUMENT)
- a containing tab pane, instance of IAccessible2_2 (IA2_RELATION_CONTAINING_TAB_PANE)
- a containing window document, instance of IAccessibleDocument (IA2_RELATION_CONTAINING_WINDOW)
- an application accessible, instance of IAccessibleApplication (IA2_RELATION_CONTAINING_APPLICATION)
Also now you can get a next and previous elements in tab order (IA2_RELATION_NEXT_TABBABLE and IA2_RELATION_PREVIOUS_TABBABLE). It's useful for AT that implement own in-page navigation (see Mozilla bug).
New IA2_RELATION_NODE_PARENT_OF is a dual relation to IA2_RELATION_NODE_CHILD_OF. It's useful to get all logical children of the accessible (as you know a logical parent-child relation may be different from parent-child relation defined by accessible tree). Example is aria-owns (like aria-owns tree) and flat structured hierarchies like XUL tree (used for message list in Thunderbird) or ARIA tree where the hierarchy is supplied by aria-level like:
<ul role="tree">
<li role="treeitem" aria-level="1">Item 1</li>
<li role="treeitem" aria-level="2">Item 1.1</li>
</ul>
See Mozilla bug.
IAccessibleDocument
IAccessibleDocument is a new interface that allows you to get an anchor target, i.e. an element that the page was scrolled to after the page was loaded. Also an object of this interface is returned by relations like IA2_RELATION_CONTAINING_DOCUMENT and IA2_RELATION_CONTAINING_WINDOW. See Mozilla bug.
Manage the media content
The idea was to manage the media content by accessible actions (IA2 group got parsimonious for a new interface so the existing mechanism was reused).
If a screen reader starts, say, a subtitled video then it invokes IA2_ACTION_OPEN action. The browsers plays a portion of subtitled video and stops it until a screen reader invokes IA2_ACTION_COMPLETE action. This action is used to notify the browser that screen reader consumed the portion of played video subtitles, for example, it finished reading of them. If screen reader is no longer interesting to manage the media playback then it invokes IA2_ACTION_CLOSE action.
If more than one AT tries to manage the same media (i.e. AT that invoked 'open' action) then the browser holds on the video playback until all AT invoke 'complete' action. See Mozilla bug.
Performance
After IAccessible2 implementation by Firefox and AT it got clear that IAccessible2 API can be improved in certain ways to make the intercommunication between the browser and AT faster. So number of changes was introduced for performance matter.
Object attribute by name
Now you can obtain object attributes by name rather than get them all together and then parse the string (see Mozilla bug).
Relation by type
Now you have a method to get relation targets by type. You don't need to get all relations when you need a single one (see Mozilla bug).
Accessible containing the caret
You have a fast way to get a text accessible containing a caret in the subtree and the caret offset in the text accessible. Previously the algorithm to find an accessible containing the caret failed on some cases. The idea of that approach was that a screen reader should crawl down the hierarchy asking for caret position until it reaches a deepest text accessible having the caret. It failed if you meet non text accessible on the way. As a workaround the screen readers navigated children. While the workaround worked well but it was really slow (see Mozilla bug).
Text attributes
The change is similar to object attributes. A light alternative to the method used to get all text attributes was added. Now you can specify a string filter and get attributes you need (see Mozilla bug).
Get all hyperlinks
Usually AT needs all hyperlinks at once. Getting them one by one is unperformant (especially for out of process AT) and requires a cache implementation on the browser side. So a new method to get all hyperlinks has been introduced (see Mozilla bug).
