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DUPLEX is ignored at run time if it is not specified on a page boundary. The printer is on a page boundary when no named or constant fields are processed for a page. After a named or constant field is processed, the printer is no longer on a page boundary. The printer is on a page boundary again when a SKIP, SPACE, ENDPAGE, or INVMMAP keyword is processed that causes the printer to move to a new page, DUPLEX, SKIP, and SPACE keywords are processed in the following order:
SKIPB
SPACEB
DUPLEX
SPACEA
SKIPA

DUPLEX is in effect only for the record format specified. After records with the specified record format are processed, the duplex value for the next record format (if the DUPLEX keyword is not specified) is the duplex specified at the file level (CRTPRTF, CHGPRTF, or OVRPRTF) command.
Option indicators are valid for this keyword.