code: private void changeDelimiters(String key) {
  
          if (key.charAt(0) != MustacheTagType.DELIMITER.getCommand()
                  || key.charAt(key.length() - 1) != MustacheTagType.DELIMITER
                          .getCommand()) {
              throw new MustacheException(
                      MustacheProblem.COMPILE_INVALID_DELIMITERS,
                      "Invalid set delimiters tag: %s [line: %s]", key, line);
          }
  
          Matcher matcher = Patterns.newSetDelimitersContentPattern()
                  .matcher(key.substring(1, key.length() - 1));
  
          if (matcher.find()) {
              delimiters.setNewValues(matcher.group(1), matcher.group(3));
          } else {
              throw new MustacheException(
                      MustacheProblem.COMPILE_INVALID_DELIMITERS,
                      "Invalid delimiters set: %s [line: %s]", key, line);
          }
      }
docs: E.g. =<% %>=, =[ ]=
  
  @param key