A subscript may be an arithmetic expression that has the value of a positive integer.
As specified in the standard, the value of an index should correspond to a valid occurrence number of the associated table. This compiler also permits corresponding occurrence numbers for 0, negative numbers, and values beyond the maximum permissible occurrence number, but the binary value of the index must remain within the range that is representable in 4 bytes, i.e. -2 ** 31 to 2 ** 31 -1. In these cases, the index must be set to a valid occurrence number before it is used (e.g. with SET UP or SET DOWN), or relative indexing must be used to ensure that only valid table elements are addressed.