The EAD standard's document type definition (DTD) specifies the elements to be used to describe a manuscript collection as well as the arrangement of those elements (for example, which elements are required, or which are permitted inside which other elements). EAD 1.0 was an SGML DTD; EAD 2002, the second and current incarnation of EAD, was finalized in December 2002 and is an XML DTD. The EAD tag set has 146 elements and is used both to describe a collection as a whole, and also to encode a detailed multi-level inventory of the collection. Many EAD elements have been, or can be, mapped to content standards (such as DACS and ISAD(G)) and other structural standards (such as MARC or Dublin Core), increasing the flexibility and interoperability of the data.