Tuesday, November 5, 2013

IAccessible2 relation API

Before IAccessible2 Mozilla practiced all manner of extensions of MSAA. I don't mean I exalt the forethought of MSAA API, I'd rather say this is an example of necessity is the mother of invention. But fortunately MSAA was extensible enough to workaround some lacks of it. Firefox ignored MSAA spec occasionally, implemented tricks and - what a surprise - some of them are in use by modern screen readers nowadays. 

All aforesaid is applicable to accessible relations. MSAA has accNavigate method to navigate the accessibles in tree hierarchy and layout order. Firefox introduced a bunch of extra constants for this method to expose accessible relations. That was a neat approach so that after IAccessible2 invention and implementation the assistive technology wasn't in hurry to switch to the right API. accNavigate was light and simple and had only one disadvantage: it didn't allow you to get multiple targets. IA2 relations in turn didn't have this limitation but API appeared heavy and Firefox implementation was quite slow those days. Firefox 4 implemented a fast version but it didn't change things. That made me think Firefox wasn't a stumbling block here. So

IAccessible2 1.3 refreshed relations API and we've got relationTargetsByType method which allows to get all targets of the given relation type. In other words this is a multiple target version of MSAA accNavigate: plain and simple. The method was implemented in Firefox 27.

I'm curious how fast the assistive technology will pick it up. Otherwise do we need those multiple targets at all?

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