Final answer:
The question references the concept of contract formation in law, specifically the 'mailbox rule', which indicates that a contract is formed when an acceptance is dispatched.
Step-by-step explanation:
The question 'A contract formed when the seller mailed the document to the buyer.' pertains to the point at which a contract is considered legally binding, which is a key concept in contract law. In many jurisdictions, a contract is formed at the moment of dispatch when using the "mailbox rule". This rule means that an acceptance of an offer becomes effective once it is sent by the offeree, as long as the communication mode is expressly or implicitly authorized by the offeror. Hence, the mailing of the contract to the buyer would constitute the formation of the contract.
Further discussions about contracts in law may include additional elements such as offer and acceptance, mutual consideration, competency, and legal intent to create a contract. For example, sellers may offer a warranty or a service contract as part of the agreement, wherein they agree to fix or replace something if issues arise within a specific time period. These are forms of additional obligations that the sellers bind themselves to, which are usually attached to the sale of significant items like cars, appliances, and houses.