History of Mark::rings 2 changes

In crates/backdrop/src/mark.rs, lines 67–71 on 3e868a1f94e111eb69563ebe52a76d3c20bfe1857f6cc65986a189b6119dd75f. 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.