We should build the infrastructure necessary to work with native accessibility services (eg. screenreaders). I imagine this being set up like the devtools; the code for communicating with the external service can exist in its own crate, with a channel per global to obtain information about the DOM and ARIA-related features. The sooner we do this basic plumbing, the harder it will be to screw it up down the road as Servo gets larger.

We can use Gecko's code as a reference here:
http://mxr.mozilla.org/mozilla-central/source/accessible/atk/Platform.cpp#124 (linux)
http://mxr.mozilla.org/mozilla-central/source/accessible/mac/mozAccessibleProtocol.h?force=1 (mac)
http://mxr.mozilla.org/mozilla-central/source/widget/cocoa/nsChildView.mm#6617 (mac)