Friday, February 24, 2012

Firefox 12 for AT developers

Firefox 12 is still on aurora channel and expected to enter into beta stage at 13 March. It doesn't have much "front-end" features but there's couple ones that might be interesting for AT developers. We did some under the hood work and crash fixes. Also we improved Mac accessibility support but it's still not a part of the default build.

ARIA support gained some sugar for multi-selectable widgets like ARIA list and tree. Now the selected state is exposed on list options and tree items by default, i.e. until aria-selected="false" is specified. This prevents screen readers like JAWS and NVDA to say "unselected" for many ARIA widgets on the web when the user traverse through their items. So a bit of sugar to keep users less annoyed.

We fixed NAVRELATION_EMBEDS MSAA relation on Firefox application accessible (ROLE_SYSTEM_APPLICATION/IA2_ROLE_FRAME). It failed to return a selected tab document accessible under certain circumstances, for example, when Firebug is installed.

Invisible and offscreen states

The most important change is we altered a logic how we expose MSAA INVISIBLE and OFFSCREEN states and ATK VISIBLE and SHOWING states. Let's do some background on this.

ATK VISIBLE means visible or the user can make it visible. ATK SHOWING means visible, i.e. on the screen. See the post  for the reference.

MSAA expectations are different. INVISIBLE means not visible on the screen (in either case), OFFSCREEN means it's not visible on the screen but the user can make it visible. See the post for the reference.

So based on that we'd need to do the following:
  • on the screen
    • MSAA: no INVISIBLE & no OFFSCREEN
    • ATK: VISIBLE & SHOWING
  • not on the screen
    • MSAA: INVISIBLE & OFFSCREEN
    • ATK: VISIBLE & no SHOWING
  • hidden accessible
    • MSAA: INVISIBLE & no OFFSCREEN
    • ATK: no VISIBLE & no SHOWING

However Firefox didn't expose hidden accessible this way on MSAA so we decided to not fix this and keep the logic closer to ATK spec:
  • on the screen
    • MSAA: no INVISIBLE & no OFFSCREEN
    • ATK: VISIBLE & SHOWING
  • not on the screen
    • MSAA: no INVISIBLE & OFFSCREEN
    • ATK: VISIBLE & no SHOWING
  • hidden accessible
    • MSAA: INVISIBLE & no OFFSCREEN
    • ATK: no VISIBLE & no SHOWING

Also we started to treat accessibles from the background as offscreen (previously they were exposed as invisible). The reason of doing this is usually ATs ignore invisible accessibles but they are interested in changes happening in background tab.

If you need more information on this then please refer to the bug to read discussion.

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