-# In case of a subdirectory filter, it is possible that a specified head
-# is not in the set of rewritten commits, because it was pruned by the
-# revision walker. Fix it by mapping these heads to the unique nearest
-# ancestor that survived the pruning.
+# If we are filtering for paths, as in the case of a subdirectory
+# filter, it is possible that a specified head is not in the set of
+# rewritten commits, because it was pruned by the revision walker.
+# Ancestor remapping fixes this by mapping these heads to the unique
+# nearest ancestor that survived the pruning.