* escape strings and concatenate the results is if you can rule out this possibility, either by
 * splitting an existing long string into short strings adaptively around {@linkplain
 * Character#isHighSurrogate surrogate} {@linkplain Character#isLowSurrogate pairs}, or by starting
 * with short strings already known to be free of unpaired surrogates.
 *

   */
  @VisibleForTesting
  static boolean validSurrogatePairAt(CharSequence string, int index) {
    return index >= 0
        && index <= (string.length() - 2)
        && Character.isHighSurrogate(string.charAt(index))
        && Character.isLowSurrogate(string.charAt(index + 1));
  }

  /**
   * Returns the given {@code template} string with each occurrence of {@code "%s"} replaced with