docs: private String performSplitting(String source, String splitString, String indexString)
          throws TransformationOperationException {
          Integer index = parseIntString(indexString, false, 0);
          Matcher matcher = generateMatcher(splitString, source);
          for (int i = 0; i <= index; i++) {
              matcher.find();
          }
          String value = matcher.group();
          if (value == null) {
              getLogger().warn("No result for given regex and index. The empty string will be taken instead.");
              value = "";
          }
          return value;
      }