Xerox 721P85530 - Manual (Page 174)

PRINT FORMAT COMMANDS
6-8 XEROX DOCUPRINT 180 LPS PDL REFERENCE
operator assistance is requested, that is, the operator or user is
requested to mount a preceding tape volume (offline) or return to
point of origin or last valid checkpoint (online).
Marker page
The system produces a marker page (refer to figure 6-1) as a function
of the input processor and inserts it into the print job at the point of
crash. It is printed after the output processor has printed data that
was already processed by input before the crash occurred.
Note: Actual size is 8.5 by 11 inches, and the squares at the top
and bottom of the page are black.