in reply to Steve Frenzel

you can detect [is Voiceover Running](developer.apple.com/documentat…)
Windows has [a flag somewhere](hanselman.com/blog/programmati…)

On the web I don't think it's so clear cut. Blind people are in two camps about this too, some argue it's not anyone's business but our own if we're running assistive technology.
my personal view is that, 9 times out of 10, you should be able to code something that works for everyone regardless.