FFF9; INTERLINEAR ANNOTATION ANCHOR
   FFFA; INTERLINEAR ANNOTATION SEPARATOR
   FFFB; INTERLINEAR ANNOTATION TERMINATOR
   FFFC; OBJECT REPLACEMENT CHARACTER

      return buildString {
        val buffer = Buffer().writeUtf8(s)
        while (!buffer.exhausted()) {
          val c = buffer.readUtf8CodePoint()
          if (c != '\\'.code) {
            append(c.toChar())
            continue
          }
          when (buffer.readUtf8CodePoint()) {
            '\\'.code -> append('\\')
            '#'.code -> append('#')
            'n'.code -> append('\n')

      writeUtf8(if (alreadyEncoded) "+" else "%2B")
    } else if (codePoint < 0x20 ||
      codePoint == 0x7f ||
      codePoint >= 0x80 && !unicodeAllowed ||
      codePoint.toChar() in encodeSet ||
      codePoint == '%'.code &&
      (!alreadyEncoded || strict && !input.isPercentEncoded(i, limit))
    ) {
      // Percent encode this character.
      if (encodedCharBuffer == null) {