Which argument is subtracted from the other by the integer-subtractfunction ?

Common sense and convention suggests that the second argument is subtracted
from the first, but given that a significant number of XACML functions have
their arguments in a counter-intuitive order, it would be best to be explicit
for functions where the order of the arguments matters.

A similar question applies to the double-subtract, integer-divide,
double-divide and integer-mod functions.

Regards,
Steven