The ALT keyword is used to indicate that the compile-time or pre-runtime array or table is in alternating format.
The array defined with the ALT keyword is the alternating array and the array name specified as the parameter is the main array. The alternate array definition may precede or follow the main array definition.
The keywords on the main array define the loading for both arrays. The initialization data is in alternating order, beginning with the main array, as follows: main/alt/main/alt/...
In the alternate array definition, the PERRCD, FROMFILE, TOFILE, and CTDATA keywords are not valid.