The other day a woman I know who shall remain nameless (she signed a non-disclosure agreement) called. “I am going to the wedding!” she cried.

“What wedding?” I said. Stupid, granted, but I had been very far away on a beach for a week. “The royal wedding,” she hissed. “What should I wear?”

It’s a difficult question: much harder, for example, than what to wear to the Costume Institute Gala (aka the party of the year), being held a mere three days later at the Metropolitan Museum of Art in New York. Parsing royal wedding attire is more complicated, I grant you, than figuring out what the highly irritating “dress festive” or “dress to sparkle” means on those holiday party invitations. It pretends to be simple – the official wedding invite instructions, apparently, were: “Wear elegant afternoon dresses with or without a coat, or an elegant matching ensemble with a hat.” (This is for women, natch; men get to wear their uniform, morning suits or just a nice formal suit.) But the reality is anything but simple.