This isn’t documented anywhere. Looking at the current (2.0.5.114) code, it looks like
DUPLICATI__EVENTNAME can be either BEFORE or AFTER
DUPLICATI__EVENTNAME
BEFORE
AFTER
DUPLICATI__OPERATIONNAME can be one of the following:
DUPLICATI__OPERATIONNAME
DUPLICATI__PARSED_RESULT can be one of the following:
DUPLICATI__PARSED_RESULT