pack("foxrmat", "f", "o", "r", "m", "a", "t")
check if the number of format chars matches the number of the parameters (ignore x), 
check if each format char (except x) has its own param with the correct length
done in parse: check unknown formats
done in func: check if length generated from calcsize is the length of generated data

unpack("foxrmat", $unpack)
done in parse: check unknown formats
done in func: check if length generated from calcsize is the length of given data