docs: static int indexOf(final CharSequence cs, final int searchChar, int start) {
          if (cs instanceof String) {
              return ((String) cs).indexOf(searchChar, start);
          }
          final int sz = cs.length();
          if (start < 0) {
              start = 0;
          }
          if (searchChar < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
              for (int i = start; i < sz; i++) {
                  if (cs.charAt(i) == searchChar) {
                      return i;
                  }
              }
          }
          //supplementary characters (LANG1300)
          if (searchChar <= Character.MAX_CODE_POINT) {
              final char[] chars = Character.toChars(searchChar);
              for (int i = start; i < sz - 1; i++) {
                  final char high = cs.charAt(i);
                  final char low = cs.charAt(i + 1);
                  if (high == chars[0] && low == chars[1]) {
                      return i;
                  }
              }
          }
          return NOT_FOUND;
      }