The MDECK option specifies that the preprocessor produces a copy of its output either on the file defined by the SYSPUNCH DD statement under z/OS, or on the .dek file under z/OS UNIX.
.-NOMDECK-. >>-+-MDECK---+-------------------------------------------------><
ABBREVIATIONS: MD, NMD
The MDECK option allows you to retain the output from the preprocessor as a file of 80-column records. This option is applicable only when the MACRO option is in effect.