MicrosStation V8i : User defined variable in project pcf of workspace

There are some variables that are described in project configuration file (.pcf) of workspace like 

XXX_GASKETS_DB = $(_USTN_PROJECTDATASET)Catalog Databases/XXXXX.mdb
XXX_ZZZ_FILES = $(_USTN_PROJECTDATASET)XXX/
XXX_SPEC_VIEW = $(_USTN_PROJECTDATASET)SpecView/

Where I can find the reference of these parameters XXX_GASKETS_DB, XXX_ZZZ_FILES, XXX_SPEC_VIEW as these are not pre-defined variables by microstation?