The following types are accepted
x        Add 'count' NUL bytes, count defaults to 1. If '?', add as much NUL bytes as specified in the cell
c        Signed character (8 bit)
C        Unsigned character (8 bit)
s/S      (Un)signed short (little endian order, 16-bit)
l/L      (Un)signed long (little endian order, 32-bit)
n/N      (Un)signed short (big endian order/network byte order, 16-bit)
p/P      (Un)signed long (big endian order/network byte order, 32-bit)
a        NUL-padded string (padded up to specified counter). If '*', simply print string and NUL-terminate
A        ASCII-padded string (paddedup to specified counter). If '*', simply print string and space-terminate
r        Raw data - inserts a string. If a counter is specified, adds that many bytes of the string, if an asterisk is specified, add all data.
@@       Jump to absolute position in packet encoder. Truncate or pad with zeroes if necessary.