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

MSG

This option controls when the compiler will issue messages for conversions that will be done via a library call.

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>>-MSG--(--+-390-+--)------------------------------------------><
 
*
Causes the compiler to issue warning messages for conversions that will be done via a library call if and only if they would be done via a library call on the platform where the code is compiled.
390
Causes the compiler to issue warning messages for conversions that will be done via a library call if and only if they would be done via a library call on 390.
Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide