code: JsonPointer append(String field) {
          RefToken[] newTokens = Arrays.copyOf(tokens, tokens.length + 1);
          newTokens[tokens.length] = new RefToken(field);
          return new JsonPointer(newTokens);
      }
docs: Creates a new JSON pointer to the specified field of the object referenced by this instance.
  
  @param field The desired field name, or any valid JSON Pointer reference token
  @return The new {@link JsonPointer} instance.