Where a state has produced a formal body of law to control recognition, this will establish a general framework under which international recognition can be managed. Where there is no formal rule within the "lex loci celebrationis", a forum court could hear expert evidence on whether the marriage would be accepted as effective (see the public policy of "favor matrimonii" which creates a rebuttable presumption in favor of the validity of any marriage) but it will be difficult for the parties to justify their failure to comply with the local laws that unambiguously would have created a valid marriage.