Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

RETURNS(BYVALUE) or RETURNS(BYADDR)

When the DEFAULT(RETURNS(BYVALUE)) option is in effect, the BYVALUE attribute is applied to all RETURNS description lists that do not specify BYADDR. This means that these functions return values in registers, when possible, in order to produce the most optimal code.

Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide