There are other, sometimes contradictory conventions. In the USA, a standard wall switch is moved "up" for on and "down" for off whereas in Europe it's the opposite. Always wondered how that came to be.
Now, let's talk about water faucets and which side is hot, and which one is cold...
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[0] - Don't know what the formal way for these are; I'm thinking of two switches hooked up in a XOR pattern to the same light - i.e. light turns on when the switches are in opposite positions, and off if they're in the same position.