code: public PeriodFormatterBuilder appendLiteral(String text) {
          if (text == null) {
              throw new IllegalArgumentException("Literal must not be null");
          }
          clearPrefix();
          Literal literal = new Literal(text);
          append0(literal, literal);
          return this;
      }
docs: Instructs the printer to emit specific text, and the parser to expect it.
  The parser is case-insensitive.
  
  @return this PeriodFormatterBuilder
  @throws IllegalArgumentException if text is null