def message_line
      begin
        if @scanner.getch == '"'
          text = message_text
          unless @scanner.getch == '"'
            err_msg = "The message text '#{text}' must be finished with the double quote character '\"'."
            raise PoSyntaxError, err_msg
          end
          skip_whitespace
          unless end_of_line
            err_msg = "There should be only whitespace until the end of line"
            err_msg += " after the double quote character of a message text."
            raise PoSyntaxError.new(err_msg)
          end
          text
        else
          @scanner.pos = @scanner.pos - 1
          err_msg = "A message text needs to start with the double quote character '\"',"
          err_msg += " but this was found: #{@scanner.peek(10).inspect}"
          raise PoSyntaxError, err_msg
        end
      rescue PoSyntaxError => pe
        raise PoSyntaxError, "Syntax error in message_line\n" + pe.message, pe.backtrace
      end
    end
def message_line
      begin
        if @scanner.getch == '"'
          text = message_text
          unless @scanner.getch == '"'
            err_msg = "The message text '#{text}' must be finished with the double quote character '\"'."
            raise PoSyntaxError, err_msg
          end
          skip_whitespace
          unless end_of_line
            err_msg = "There should be only whitespace until the end of line"
            err_msg += " after the double quote character of a message text."
            raise PoSyntaxError.new(err_msg)
          end
          text
        else
          @scanner.pos = @scanner.pos - 1
          err_msg = "A message text needs to start with the double quote character '\"',"
          err_msg += " but this was found: #{@scanner.peek(10).inspect}"
          raise PoSyntaxError, err_msg
        end
      rescue PoSyntaxError => pe
        raise PoSyntaxError, "Syntax error in message_line\n" + pe.message, pe.backtrace
      end
    end
identifies a message line and returns it's text or raises an error

 @return [String] message_text