anchor.diff:  
   -export([parse/2, usage/2, usage/3, usage/4]).
   
  +-export_type([arg_type/0,
  +	      arg_value/0,
  +	      arg_spec/0,
  +	      simple_option/0,
  +	      compound_option/0,
  +	      option/0,
  +	      option_spec/0]).
   
   -define(TAB_LENGTH, 8).
   %% Indentation of the help messages in number of tabs.
  
positive.code:     (Arg =:= "on") orelse (Arg =:= "enabled") orelse
      (Arg =:= "1").
  
      
  -spec is_arg_false(string()) -> boolean().
  is_arg_false(Arg) ->
      (Arg =:= "false") orelse (Arg =:= "f") orelse
  
negative.code:         _ ->
              throw({error, {missing_option_arg, Name}})
      end.
  
  
  %% @doc Find the option for the discrete argument in position specified in the
  %%      Pos argument.
  