About Fog-light rule: rain versus fog: which statement is WRONG?
You may not switch on the rear fog light in rain, not even during heavy rain showers: the bright red light and its reflection actually hinder following traffic.
As soon as it rains, you are required to switch on your front fog light, just like your dipped beam.
Only use the rear fog light if it improves safety; if following traffic has already seen you, the bright rear fog light actually hinders them. 'Keep it on until the fog is gone' is not a book rule.
Only switch on the rear fog light when it is better for safety; if following drivers have already seen you, the bright light is a nuisance to them.
Explanation
trap: 'may' read as 'must'. Book p.187 - dipped beam is always mandatory in rain; the front fog light may only be switched on during heavy rain that seriously impairs visibility (visibility less than about 200 m). In ordinary light rain the front fog light is not required