Since the topic of PREP_PROCESS_VAR within the 11.2 documentation is missing, special thanks for the headsup from
FrankMuffke please find the link to this topic within 11.1 documentation.
Since there was no significant change on that script command between these versions, this can be used for 11.2 too:
https://docs.automic.com/documentation/webhelp/english/ALL/components/AE/11.1/All%20Guides/help.htm#ucaasc.htm?Highlight=PREP_PROCESS_VARWe have forwarded this to our documentation team already, till it is fixed, this topic might help you out.