Function stored_answered 

pub fn stored_answered(text: &str, me: &str, answer: &str) -> String

An invitation’s event as your calendar keeps it once you answered: as the organizer sent it (stored), your own line among the guests (me, by address) saying your answer (“ACCEPTED”, “TENTATIVE”), as an attendee’s copy says it (RFC 5546 §3.2.3). Your other devices, and any calendar reading the server, then know what you answered; two devices answering the same invitation can tell whether they said the same (answers). Unchanged but for METHOD when you are not among the guests by that address.