Respect for age is de rigueur at all times, like clean hands.
It is de rigueur that he should carry some piece of iron on his person.
In those days handwriting and spelling were not "de rigueur."
It was de rigueur for ladies to conceal their faces with fans.
It may be added that a spirit lamp beneath the dish is (or should be) de rigueur.
The green paint is de rigueur; ...