Salary includes the following kinds of allowances:
(a) an allowance in respect of the possession of certain qualifications;
(b) an allowance in respect of the performance of duties additional to the ordinary duties of an office or position, not being an allowance in respect of the performance of such duties for a temporary period;
(c) an allowance in lieu of quarters;
(d) an allowance payable to a person as an officer-in-charge.