anchor.diff:      %% Either...
     ].
   
  -optional_match_test_() ->
  +match_optional_test_() ->
     OA = opt("-a"),
     OB = opt("-b"),
     OX = opt("-x"),
  
positive.code:      (_)                    -> false
    end.
  
  option_match_test_() ->
    A  = opt("-a"),
    AT = A#option{value = true},
    X  = opt("-x"),
  
negative.code:   , ?_assertEqual({true , [V0]    , [AV]}, match(A, [V, V0]))
    ].
  
  match_command_test_() ->
    C  = cmd("c"),
    A  = arg(undefined, "c"),
    CT = cmd("c", true),
  