I expected the two common side mouse buttons (Mouse4 and Mouse5) to be referenced by MouseButton::Other(1) and MouseButton::Other(2) (or by 4 and 5), but they are currently referenced by MouseButton::Other(32) and MouseButton::Other(64).

I believe this is a relatively recent change (and perhaps unintended?), as I had been referring to them previously using 1 and 2 (in a Bevy 0.8 project).