Screen-reader support

[iamahuman]

The problem you're addressing (if any)
Supporting screen-reader technology while maintaining the security promises of Qubes, to make it more accessible.

Describe the solution you'd like

• Install accessibility tools inside of each VM
  • Pros: least effort, less new code.
  • Cons: This means that the audio from each VM shall be distinguishable as it is with GUI.
    • By letting the user specify the Qube that shall "talk," with a dedicated "secure attention key" that will mute it. (easiest to implement)
    • By preceding audio with (out-of-band) identification information, so that VMs not receiving attention can still send notifications.
    • If allowing two or more simultaneous stream to play, by somehow "modulating" that information into the PCM stream suitable for auditory perception (pitch shifting, etc).
    • The stereo nature of hearing might somehow be exploited, at the cost of decreased accessibility.
• Multiplex accessibility tree and content components
  • Note: In Linux desktop, D-Bus AT-SPI2 protocol is the de facto standard.
  • Pros: flexibility over how the screen information may be rendered, can get rid of both video and audio channel in such use cases.
  • Cons: need to implement separate forwarding bridge and multiplexer (over vchan or qrexec) which means more code; plus, OSes that do not use AT-SPI2 would need translation.

Where is the value to a user, and who might that user be?
Visually impaired users may benefit most, while this feature is available to any user.

Describe alternatives you've considered
Resolving #1596 will let users implement the first option by themselves, albeit possibly to a limited extent.

Additional context
This is a follow-up to #1596.

Also ought to be considered is that this targets an entirely new user base, not the existing one. Even if this feature is implemented, failure to market and/or appeal to possible beneficiaries (perhaps even more difficult than the technical problem) will bury all efforts to nil.

Relevant documentation you've consulted
None.

Related, non-duplicate issues

• better accessibility support - install accessibility tools by default in dom0 and templates #1596 (blocker)
• Provide colorblind options for State column in Qube Manager #1533 (to a lesser extent)