PLISRTA, PLISRTB, PLISRTC, and PLISRTD are built in functions that allow calls to sort from within PL/1. Which one you use depends on whether you require a presort or postsort procedure to be called from within the sort process.
PLISRTA is rarely used because it does not allow you to perform any processing on the records to be sorted.
PLISRTB allows you to perform processing on the records before they are sorted.
PLISRTC allows you to perform processing on the records after they are sorted.
PLISRTD is the most commonly used because it allows you to perform processing on the records both before and after the sort.
This article written by Stephen Chapman, Felgall Pty Ltd.