Accessibility (UIA) Troubleshooting

Chromium-based browsers offer a number of accessibility-related features. When you visit about:accessibility, you can see more about the state of these features (similarly, you can find the states in about:histograms/Accessibility.ModeFlag). You can enable features via the Accessibility page, or by You can also passing the command line argument --force-renderer-accessibility into the browser.

In some cases, you may be surprised to find some of the accessibility features enabled even when you have not manually enabled them:

This can happen when the browser detects interactions from a UI Automation tool; such API calls are mostly from accessibility tools like screen-readers. However, some features like Windows 10’s Text Cursor Indicator:

…are implemented using UIA, and when this feature is enabled, the browser enables the corresponding accessibility features.

Back in the spring, some improvements to the Accessibility code caused a series of regressions that would result in crashes, hangs, and memory exhaustion when a loading many pages, including YouTube:

These regressions were impactful for many customers who didn’t expect to be running the impacted code. Fortunately, the problems were quickly fixed.

Unfortunately for end-users, tracking down how Accessibility features got enabled on their browsers is presently used to be non-trivial. (Update: read on)

For Microsoft Edge users running Windows 10 version 20H1 or later, visiting about:histograms/UIA will show a truncated hash of the process name of the UIA client:

The value shown is the Integer representation of the first four bytes of the SHA-1 Hash of the process name. Some common values include:

Truncated HashProcess Name
612857738EoAExperiences.exe (Win10 Text Cursor Indicator feature)
1759000766TextExpander.exe
319076627Narrator.exe
427450884Snagit32.exe
592588840Magnify.exe
3897604127magnify.exe
494880639nvda.exe

Unfortunately, there’s no easy way to go from a truncated hash back to the original string; hashes are one-way. (The only way to do it is brute force — start with a list of possible strings and hash them all to find a match).

A simple PowerShell script mostly written by Artem Pronichkin allows you to get the hashes of all of your running processes, which you can then compare to the reported value:

In the future, we hope to streamline this experience somewhat, but for now, it’s an annoyingly geeky scavenger hunt.

Update: In Edge 93+, the edge://accessibility page includes a simple “Show Client Info” button. Easy peasy.

Published by ericlaw

Impatient optimist. Dad. Author/speaker. Created Fiddler & SlickRun. PM @ MSFT '01-'12, and '18-, presently working on Microsoft Edge. My words are my own.

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