+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| 1 1| OFFSET |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The first two bits are ones. This allows a pointer to be
distinguished from a label, since the label must begin with two zero
bits because labels are restricted to 63 octets or less. (The 10 and
01 combinations are reserved for future use.) The OFFSET field
specifies an offset from the start of the message (i.e., the first
octet of the ID field in the domain header). A zero offset specifies
the first byte of the ID field, etc.