code: protected void parse (String arg, Argument argDesc)
          throws YarrgParseException
      {
          Parser<?> parser = parsers.get(argDesc.field);
          if (parser == null) {
              parser = _cmd._factory.createParser(argDesc.field);
              parsers.put(argDesc.field, parser);
          }
          try {
              parser.add(arg);
          } catch (RuntimeException e) {
              throw new YarrgParseException(_usage, e.getMessage(), e);
          }
      }
docs: Adds the value from arg to the parser for argDesc.