Wednesday, February 8, 2012

Firefox 11 for AT developers

Here's an update what's new in Firefox 11 (beta, release on March 13) for assistive technology developers.


CSS generated tables (CSS display:table style) are exposed as layout tables. Originally this piece of work was targeted to Firefox 10 but we weren't in time to make this happen.

HTML table cells (HTML th and td elements) gained new not standard axis and abbr object attributes.

The axis object attribute is direct mapping of HTML @axis attribute. This object attribute is supposed to help AT to extract semantic of rich HTML tables in the web. Granted, this HTML attribute is not wide used on the web but we wanted to break the chicken-egg problem: browsers/AT don't support it iff web authors don't use it.

The abbr object attribute is less academic than previous one and useful to pick up short accessible name for header cells, for example, it makes sense when the user traverses through table cells and screen reader announces related heading information for each cell. The user doesn't want to hear long header cell names on and on: that's what abbr object attribute is supposed to help to. This object attribute is exposed in two cases:
  • HTML abbr element is inside the table cell
  • @abbr attribute is used on table cell
  <th id="th1"><abbr title="Social Security Number">SS#</abbr></th>
  <th id="th2" abbr="SS#">Social Security Number</th>

HTML acronym and abbr elements allow @title attribute for accessible name computation. This can be illustrated by following example:
  <input id="input">
  <label for="input"><acronym title="O A T F">OATF</acronym></label>
Accessible name of input accessible is "O A T F" now.


HTML5 figure and figcaption elements are now accessible.  The figure element is exposed with generic MSAA ROLE_SYSTEM_GROUPING and ATK ATK_ROLE_PANEL roles because neither IAccessible2 nor ATK provide more suitable roles. AT can rely on xml-roles:figure object attribute to detect figure element. HTML figure element picks up accessible name from figcaption element which is exposed with IA2_ROLE_CAPTION / ATK_ROLE_CAPTION role. The figure and figcaption accessible objects are linked by LABELLED_BY / LABEL_FOR relations.

The content of HTML5 canvas element is not accessible still but Firefox 11 started to expose an accessible object having IA2_ROLE_CANVAS/ATK_ROLE_CANVAS role for canvas element itself. Not big deal but it's a good first step on canvas accessibility.


ARIA attributes used on HTML file element (input@type="file") are propagated to underlying text field and "Browse" button, i.e. accessible states defined by these attributes are inherited.

ARIA combobox (@role="combobox") fires MSAA EVENT_OBJECT_VALUECHANGE event and ATK accessible-value signal when option is changed. Here's an example of ARIA combobox widget.


IA2_STATE_ACTIVE/ATK_STATE_ACTIVE state is exposed on active item for standard composite widgets like HTML select elements. The state can be used for example to detect the current item of the widget when the widget isn't focused. We make our implementation closer to ARIA widgets where aria-activedescendant technique is used. Another side of this code unification is IAccessible::accSelect called with SELFLAG_TAKEFOCUS flag can be used on widget items now.

Small fix for IAccessible::get_accName that returns S_FALSE when the accessible object doesn't have accessible name. Not big deal. Done for consistence and meet MSAA spec.

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