The traditional phrase "signed, sealed and delivered" refers to the practice of seals; however, attesting witnesses have replaced seals to some extent. Agreements under seal are also called contracts by deed or "specialty"; in the United States, a specialty is enforceable without consideration. In some jurisdictions, specialties have a liability limitation period of double that of a simple contract and allow for a third party beneficiary to enforce an undertaking in the deed, thereby overcoming the doctrine of privity. Specialties, as a form of contract, are and can therefore be distinguished from covenants, which, being also under seal, are unilateral promises.