They don’t have to. There’s the law and there’s bylaw.
In contractual law it is very normal to stipulate all those terms and agreements between parties and then refer to the code of (civil) law for all those legal requirements overseeing and enforcing the contract. “For all other terms and conditions parties refer to the Dutch Civil Code of Justice”, where it can be enforced.
And… Word to the wise… There’s a good reason why the Romans originally, and Napoleon thereafter in his Code Civil, excluded most elements of Commerce Law of the General Civil Law and assigend them to their own Chamber instead; because in contractual law mutually willing people can go very far in agreeing to their own terms and conditions as long as there’s contractual consent.
So, might wanna reconsider on offering up your first born. Just to be sure… 