selected documents within a collection or group of records, if the research value is deemed to be extremely high, heavy use is expected, or the risk of theft is heightened. Finding aids The written description of a collection is generically termed a finding aid. The main purpose of a finding aid is to facilitate access to a collection of materials by users, and can also useful for other archivists who provide reference services to the materials currently and in the future. The earliest finding aids were known as "calendars" and generally consisted of a listing of individual documents in chronological order, which was the preferred organizational method of historians, who were their primary users at the time. Currently used forms of finding aids vary in length and fall into several categories by type, with the inventory predominating in the late 20th and early 21st centuries. Many archives post their finding aids online to widen exposure to their holdings and some are encoded (see Standards section below) to facilitate recognition by web search engines. Standards Several standards govern archival description, some national and some international. ISAD(G), the General International Standard Archival Description, defines the elements that should be included in a finding aid. Other content standards also pertain. In the United States, proper names may be checked against the Library of Congress Name Authority Files and subject headings are drawn from the LCSH. Genre terms are often taken from the Art & Architecture Thesaurus. Many finding aids are encoded (marked up) in XML; in such cases, the Encoded Archival Description (EAD) standard can be used. In addition, repositories may follow local practices designed to make finding aids serve their particular mission. The Society of American Archivists (SAA) has published a number of best practices for American archivists; two important ones are Archives, Personal Papers and Manuscripts, often abbreviated as APPM, and Describing Archives: A Content Standard (DACS). SAA's publication Standards for Archival Description: A Handbook provides an overview of relevant standards for all phases of archival and manuscripts processing. The Research Libraries Group has published a best practices document for use with EAD. The Archives and Records Association, the British equivalent of the SAA, has published a number of best practices for U.K. archivists on topics ranging from school records retention to historical accounting records. The Australian Society of Archivists published Describing Archives in Context: A Guide to Australasian Practice in