The main contracts and security contracts are active simultaneously and, in some cases, the provisions of these contracts may replace the provisions of the former. For example, companies X and Y enter into a construction contract with X as the owner and Y as the owner. It then enters into a secondary contract with Z, a hardware supplier. If the materials are found to be defective, X Z can sue when they do not have a contract between them. A support contract is a contract by which the contracting parties enter into or promise another contract. The two treaties are therefore linked and can be applied, even if they are not a constructive part of the original treaty.  In JJ Savage and Sons Pty Ltd v. Blakney, a mere expression of opinion was not deemed sufficient to be kept as a promise. In Crown Melbourne Limited v Cosmopolitan Hotel (Vic) Pty Ltd, a statement from a landlord to the tenants considered when negotiating a lease agreement that they are “supported during the extension” would not bind the lessor to offer another five-year lease.  A theory confirms that it is possible to qualify the establishment of an auxiliary contract for a third-party beneficiary, since the letters of credit are brought, by the necessity of the purchaser and in according the theory of Jean Domat, to the cause of a letter of credit, that a bank issues a credit to a seller in order to exempt the buyer from his obligation to pay directly to the seller with a legal offer.
There are three different companies involved in the letter of credit transaction: the seller, the buyer and the banker. Therefore, an accreditation contract is theoretically understood as a guarantee contract, which is accepted by a behaviour or, in other words, as a tacit contract.  It is briefly called LOC When used, it is important to ensure that they are fully documented and that they comply with contract formation rules. Otherwise, it is likely that the incidental comparison will be legally unenforceable. The Common Law recognizes the collateral contract as an exception to the Parol rule of evidence, which means that the evidence authorized for a companion contract can be used to exclude the application of the Parol rule of evidence. In practice, it is rare to regard the warranty contract as an exception, as it must be strictly proven; and the burden of proof will only be lightened if the purpose with which the main contract is entered into is more unusual.  Ancillary contracts are an exception to the practice of treaty doctrine which states that a contract cannot impose obligations or rights on an unrelated party.  However, in cases where a security contract is entered into between a third party and one of the contracting parties, the Court may authorize rights or obligations to the non-contracting party, as outlined in the previous unauthorized Donoghue/Stevenson case.  With a two-part security contract, the two parties entering into the main contract also enter into the security contract. A tripartite support contract includes a debt statement of a third party that does not participate in the original contract. this.
B is often used in the case of a sales contract. The consideration is a contractual requirement under the common law and means that each party must bring something valuable to the table. When a party intends to legally enforce a contract, it must prove that it has performed a performance or that it has suffered harm. Money can sometimes be used as a match, but it is not always enough. Consideration does not necessarily have to be a fair and legal exchange, but must be deemed appropriate by the court.