Article 6 guarantees party autonomy over both the conflict rules and the substantive law. On the basis of proposals from Anglo-Saxon countries,[93] a fundamental issue much debated in UNCITRAL reappeared, namely whether the parties must affirmatively choose CISG in order for it to apply (the so-called "opting-in" solution) or whether the Convention would automatically apply, unless the parties agreed to apply a different law (the "opting-out" solution).[94] In the end, the "opting-in" proposal, which would have turned the Convention into a set of standard contract terms, was rejected, as was the demand to include a reservation clause in the Final Provisions, as had been done in ULIS.[95]
Also rejected was a Canadian proposal to exclude certain principles, such as the standard of good faith, from the domain of the party autonomy.[96]
The Convention can be excluded by choice of law if the parties choose to apply a different local domestic law. It is also possible simply to reject CISG without choosing an applicable law. Substantively, any rule of the Convention can be altered or rejected by the parties, even by standard contract terms,[97] as long as the requirements for their validity in domestic law are fulfilled.