History of Mark::rings 2 changes

In crates/backdrop/src/mark.rs, lines 67–71 on 8a48dd83017887dd6e31775ac1ad4684d223e9932110c29841b8eb63fbd21449. Every change that wrote or deleted one of these lines, or deleted a line from between them. Exact, because each line keeps its identity across edits; edits elsewhere in the file are not here. Also: oxy log -L 67,71:crates/backdrop/src/mark.rs.