docs: private static void escapeRegexpRangeOnto(char start, char end, StringBuilder out) {
      if (!isPrintable(start)) {
        out.append(String.format(start >= 0x100 ? "\\u%04x" : "\\x%02x", (int) start));
      } else {
        out.append(EscapingConventions.EscapeJsRegex.INSTANCE.escape(String.valueOf(start)));
      }
      if (start != end) {
        // If end - start is 1, then don't bother to put a dash.  [a-b] is the same as [ab].
        if (end - start > 1) {
          out.append('-');
        }
        if (!isPrintable(end)) {
          out.append(String.format(end >= 0x100 ? "\\u%04x" : "\\x%02x", (int) end));
        } else {
          out.append(EscapingConventions.EscapeJsRegex.INSTANCE.escape(String.valueOf(end)));
        }
      }
    }