Question: How to create two mutually exclusive contexts?

[anohren]

I have two contexts, "daytime" and "nighttime". Nighttime's active state is controlled by the system clock.

It's easy to express that daytime is active with 100% confidence whenever nighttime is not active. But how do I express that daytime is not active with 100% confidence when nighttime is active? Without it I'll eventually end up with both contexts active.

I have other contexts as well so it's not a solution to disable multiple active contexts.