Function tombstone_of 

pub fn tombstone_of(
    current: &Record,
    now_ms: i64,
    cap: usize,
    author: Option<&Identity>,
) -> Record

The tombstone that deleting the live record current produces. author, when given, is the deleter and replaces meta.author; otherwise the tombstone keeps the last live writer’s metadata.

A delete is a write, so meta.updated becomes the delete’s time while meta.created stays the deleted record’s (gonzalo#293). deleted_at is the same instant, and is what collection reads.