History of Mark::rings 2 changes

In crates/backdrop/src/mark.rs, lines 67–71 on b1860d6090ec974c444d35bae685fd50cdd7748e2cf00222d5c83dbb79c7c20d. 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.