anchor.diff:  
   % Fetch values and defaults
   fetch_value(vars, Opts) -> opt_or_default(vars, [], Opts);
  +fetch_value(user, Opts) -> opt_or_default(user, undefined, Opts);
   fetch_value(env_vars, Opts) -> opt_or_default(env_vars, [], Opts);
   fetch_value(num_processes, Opts) -> opt_or_default(num_processes, "5", Opts);
   fetch_value(files_count, Opts) -> opt_or_default(files_count, "5", Opts);
  
positive.code:     FilesCount,
      Mount,
      Env,
      " ",
      Command
    ]).
  
negative.code:   ProcessCount = build_cli_option("-p", num_processes, Opts),
    FilesCount = build_cli_option("-f", files_count, Opts),
    Mount = build_cli_option("-i", image, Opts),
    User = build_cli_option("-u", user, Opts),
    
    lists:flatten([
      babysitter:isolate_command(), 
      ConfineDirectory,
      SkelOrDirs,
  