-Unless `--octopus` is given, among the two commits to compute the merge
-base from, one is specified by the first commit argument on the command
-line; the other commit is a (possibly hypothetical) commit that is a merge
-across all the remaining commits on the command line. As the most common
-special case, specifying only two commits on the command line means
-computing the merge base between the given two commits.
+OPERATION MODE
+--------------
+
+As the most common special case, specifying only two commits on the
+command line means computing the merge base between the given two commits.
+
+More generally, among the two commits to compute the merge base from,
+one is specified by the first commit argument on the command line;
+the other commit is a (possibly hypothetical) commit that is a merge
+across all the remaining commits on the command line.