anchor.diff:        // TODO: ArgParser.parse throws FormatException which does not indicate
         // which sub-command was trying to be executed.
         var helpUsage = e is UsageException ? e.usage : usage;
  -      print('$e\n');
  -      _printHelp(helpUsage);
  -      exitCode = 2;
  +      _handleUsageError(helpUsage, e);
         return;
       }
   
  
positive.code:   /// Handles successfully validated [commandInvocation].
    _handleResults(CommandInvocation commandInvocation);
  
    /// Prints help information for the associated command or sub-command thereof
    /// at [commandPath].
    // TODO: Integrate with Loggers.
    _printHelp(Usage helpUsage) {
      print(getUsageFormatter(helpUsage).format());
    }
  
    bool _checkHelp(CommandInvocation commandInvocation) {
  
negative.code:     if(commandInvocation == null) {
        // TODO: Move this to an earlier UsageException instead ?
        if(usage != null && usage.commands.isNotEmpty) {
          _handleUsageError(usage, 'Must specify a sub-command.');
        }
        return;
      }
  