code: private static String getRegexp(SedArguments args)
     {
        if (args.isRegexpSet())
        {
           return args.getRegexp();
        }
        if (args.isString1Set())
        {
           return args.getString1();
        }
        return "";
     }
docs: Returns the regexp operand from args, either called "regexp" or
  "string1". If none of the two is set, an empty string is returned.
  
  @param args
  the args with operand values
  @return the regexp argument from "regexp" or "string1" or an empty string
  of none of the two operands is set