Document written in Standard Generalized Markup Language (SGML); includes tags that describe the information's structure and content; may contain multiple types of information, such as text, graphics, database information, and even audio and video data. SGML files are similar to .XML files in that they reference Document Type Definition (.DTD) files, which describe the tags used within the document.
Encoded Archival Description is an XML standard for encoding archival finding aids, maintained by the Library of Congress in partnership with the Society of American Archivists.