code: private PatternConstant create(Constant constant) {
          if (!constants.containsKey(constant)) {
              constants.put(
                      constant,
                      new PatternConstant(constant.getValue(), constant.isIgnoreCase(), constant.isGhost())
              );
          }
          return constants.get(constant);
      }
docs: Create a constant element for text parsing
  
  @param constant constant definition
  @return pattern element for constant