Letters patent (always in the plural) are a type of legal instrument in the form of a published written order issued by a monarch, president, or other head of state, generally granting an office, right, monopoly, title, or status to a person or corporation. Letters patent can be used for the creation of corporations or government offices, or for the granting of city status or a coat of arms. Letters patent are issued for the appointment of representatives of the Crown, such as Governors and Governors-General of Commonwealth realms, as well as appointing a Royal Commission. In the United Kingdom they are also issued for the creation of peers of the realm. A particular form of letters patent has evolved into the modern patent (referred to as a utility patent or design patent in United States patent law) granting exclusive rights in an invention (or a design in the case of a design patent). Clearly in this case it is essential that the written grant should be in the form of a public document so other inventors can consult it to avoid infringement and also to understand how to "practice" the invention, i.e., put it into practical use.