An illustration of this rule can be found in a case in which the Supreme Court of France ruled that legitimate heirs could demand the reduction of a hidden gift contained in a letter signed by their author. However, in some situations, it is necessary to disclose letters of support for reasons of transparency. This may be the case, for example. B, for investors or even for third parties. In writing, it may be useful to change the terms defined in the primary contract. In the case of International Milling Co v. Hachmeister Inc., the parties to a sales contract used a letter to modify the quality requirements of the product delivered to make them more restrictive than the terms of the primary contract. The preamble and confidentiality clause of a mailing note are also essential concepts.
Some do not apply to all agreements (I), others only apply to some (II). In share purchase contracts, ancillary letters are sometimes added to presentations and guarantees to deal with issues such as tax debts or social issues that contracting parties do not want to know that the authorities are aware of.