Like, for instance, middle-clicking browser links. It's still a thing!
When you're putting clickable elements on your single page apps, but don't make them <a> tags with an href, maybe you'll go through the trouble to detect a ctrl+click to open in a new window, but forget to test for mouse3 clicks too. :(
(I admint I have been guilty of this.)
I've clocked a lot of time reaching behind the computers to transplant the keyboard for 30 seconds, just to open a link in a new browser tab.
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