rigid type III (verb-final) … Conjunctive verb form. There is a frequently-used, non-final verb form, a “conjunctive”, with the semantic value ‘having done such-and-such’ or ‘do (did) such-and-such and …’ which appears in subordinate clauses.
Standardized
IF basic order is OV, THEN a frequently-used kind of subordinate clause is one with conjunctive verb forms.