[TCLCORE] Making Tk accessible for screen readers

[Kevin W. <kw...@co...>]

A feature that is requested from time to time is to make Tk accessible 
for screen readers for users who are blind. The last ticket I found on 
this was 
https://core.tcl-lang.org/tk/tktview/0e294d9604b4196b9ca41451400730063a659c70, 
from 2016.

I've looked into this a bit and it seems to be a massive undertaking. 
For it to work cross-platform, it would require access to three 
platform-specific API's, and would likely require an internal API as 
well to provide some abstraction.

Here are some some rough notes:

1. On Linux, it would require implementing ATK, the Gnome Accessibility 
Toolkit, documented at 
https://en.wikipedia.org/wiki/Accessibility_Toolkit and 
https://developer.gnome.org/atk/. This would implement a "server-side" 
API that Tk would provide, and would be bridged on Gnome by another 
library (at-spi) that the Orca screen reader makes use of. ATK 
supposedly provides a series of abstract header files that would allow 
other libraries to implement the API - this might avoid license issues 
that would otherwise be present (Gnome is LGPL, I believe).

2. On Windows, the iaccessible2 API (documented at 
https://en.wikipedia.org/wiki/IAccessible2 and 
https://accessibility.linuxfoundation.org/a11yspecs/ia2/docs/html/) 
provides a BSD-licensed layer over Microsoft's platform-native API, 
designed to provide an API similar to ATK to make cross-platform 
accessibility easier to achieve.

3. On macOS, the NSAccessibility API (documented at 
https://developer.apple.com/library/archive/documentation/Accessibility/Conceptual/AccessibilityMacOSX/index.html#//apple_ref/doc/uid/TP40001078-CH254-SW1 
and 
https://developer.apple.com/documentation/appkit/accessibility/integrating_accessibility_into_your_app?language=objc) 
provides a complete set of tools for making apps accessible on the Mac.

OpenOffice's internal accessibility API, UNO, provides a model of how a 
cross-platform accessibility API can be implemented. Recent versions of 
OO use the Apache license, which would work just fine with Tcl/Tk's 
license. The UNO API is bridged to ATK on Linux, Java's Accessibility 
API on Windows, and NSAccessibility on Mac. Of course UNO's specifics 
could not be ported to Tk, but the API itself might provide an example 
structure for Tk.

I've been mulling taking on this project, as it is the largest part of a 
modern UI system that Tk lacks compared to other toolkits. I am 
estimating a couple of years of work, though, and that is giving me 
pause. Accessibility in OO was developed by an entire team at Sun before 
it was disbanded, not a single person. Is there any interest in the 
community for this type of project?

--Kevin

-- 
Kevin Walzer
Code by Kevin
http://www.codebykevin.com