docs: function _appendMappedString(formatString, mapping, beginIndex, currentIndex, resultString) {
    let tempString;
  
    if (beginIndex !== -1) {
      tempString = formatString.substring(beginIndex, currentIndex);
      // check if the temporary string has a known mapping
      if (mapping[tempString]) {
        tempString = mapping[tempString];
      }
      resultString = resultString.concat(tempString);
    }
    return resultString;
  }