In English law, a purpose trust is a trust created for the fulfillment of a purpose, not for the benefit of a person. These are normally considered invalid by the courts because they have no legally recognized beneficiaries, therefore nobody to enforce the trust, with the exception of charitable trusts, which are enforceable by the Attorney General as they represent the public interest. As well as charitable trusts, there are several exceptions to the rule against purpose trusts. If the requirement to fulfill a purpose is a request, rather than an obligation, the trust is valid; a trust will also be found valid if, while being for a purpose, it involves beneficiaries in some respect. Purpose trusts can also be valid if they are for the erection or maintenance of tombs and memorials (assuming such memorials are not overly grandiose), the maintenance of animals, and arguably the saying of masses, although these must all obey the rule against perpetuities and not continue for more than 21 years after the testator's death.