+Note that global bootmeths introduce a subtlety into the above description.
+When `doing_global` is true, the iteration takes place only among the bootmeths,
+i.e. the last column above. The global bootmeths are at the end of the list.
+Assuming that they are entries 3 and 4 in the list, the iteration then looks
+like this:
+
+ ======== ======= ======= =======================================
+ bootdev part method notes
+ ======== ======= ======= =======================================
+ . . 3 doing_global = true, method_count = 5
+ . . 4
+ 0 0 0 doing_global = false, method_count = 3
+ 0 0 1
+ 0 0 2
+ 0 1 0
+ 0 1 1
+ 0 1 2
+ 1 0 0
+ 1 0 1
+ ...
+ ======== ======= ======= =======================================
+
+The changeover of the value of `doing_global` from true to false is handled in
+`iter_incr()` as well.
+