docs: public static void appendMailto (final StringBuilder out, final String in, final int start, final int end)
    {
      for (int i = start; i < end; i++)
      {
        final char c = in.charAt (i);
        final int r = rnd ();
        switch (c)
        {
          case '&':
          case '<':
          case '>':
          case '"':
          case '\'':
          case '@':
            if (r < 512)
              _appendDecEntity (out, c);
            else
              _appendHexEntity (out, c);
            break;
          default:
            if (r < 32)
              out.append (c);
            else
              if (r < 520)
                _appendDecEntity (out, c);
              else
                _appendHexEntity (out, c);
            break;
        }
      }
    }