o Code simplification and refactoring:
    - Do not use SMARTLIST_FOREACH for any loop whose body exceeds
      10 lines. Doing so in the past has led to hard-to-debug code.
      The new style is to use the SMARTLIST_FOREACH_{BEGIN,END} pair.
      Issue 6400.
    - Do not nest SMARTLIST_FOREACH blocks within one another. Any
      nested block ought to be using SMARTLIST_FOREACH_{BEGIN,END}.
      Issue 6400.