Physical vs character
KeyQ is a position. The glyph you get depends on layout, Shift, and dead keys. If you are on AZERTY or a laptop that remaps Fn, the label on the drawing may not match the legend on the hardware. The code field is still the one to trust for “is this switch firing.”
Tab, Alt, and Meta are prevented from stealing focus so the tester stays in the page. Escape still belongs to the browser chrome in some environments.
FAQ
What is which?
Legacy keyCode. Useful when you are matching old docs. Prefer code for new work.
Stuck key?
If a key stays lit after release, the OS is repeating a down without an up — or you tabbed away mid-hold. Blurring the window clears the map.