docs: protected String getUserDefinedFieldName(String field) {
          int index = field.indexOf('-');
          char letter = getUserDefinedFieldLetter();
  
          for (int i = 0; i < index; ++i) {
              if (field.charAt(i) == letter) {
                  return field.substring(index + 1);
              }
          }
  
          return null;
      }