From a reader…
I’m unlearned in the extraordinary form, and the other day, I saw the MC clap his hands when the servers were supposed to kneel. Is that common? I thought it was a little odd.
Yes, a handclap is a typical signal given by a Master of Ceremonies. It shouldn’t be loud, just loud enough to be heard. Some MCs will have a different number of claps for different movements, but that seems unnecessary to me: servers and sacred ministers should know what’s coming next.