Microsoft Access Form default filter not passed but working -

i have existing ms access application. access application contains summary list data driven , when double click row, opens entry form. in entry form, searches drilled down record , displays selected item summary screen on entry form's form_open.

however, there no code parameter primary key passed when doing docmd.openform. there no filter or wherecondition when query being selected in dbengine.workspaces(0).databases(0).openrecordset("tablename", dbopendynaset).

i not familiar ms access, parameter being passed automatically?