(dupe of other comment in same thread by me)

For OS X at least...

https://www.hcs.harvard.edu/~jrus/site/cocoa-text.html

If you haven't yet tweaked these "not well-advertised" settings, this may indeed turn out to be a "this changes everything!" moment for you

I guess he's picking the apps that support that - probably web browser via extension, and cli apps which often do that.