The Hong Kong Identity Card (HKID) contains a person´s HKID number, of which the standard format is X123456(A)

X represents one (1) or two (2) letters of the alphabet. 

Numerals may represent a Arabic number. 

A is the check digit, which has 11 possible values from 0 to 9 and A. 

The letters and numbers are not assigned arbitrarily.