<DID> should not be considered optional

"Imagine a typical scenario: An archivist begins encoding a finding aid by first opening the EAD element and creating the required EADHEADER. He or she may add some FRONTMATTER before opening the ARCHDESC element and setting its LEVEL attribute to the value "collection," "record group," "fonds," or "series," depending on which term best reflects the character of the whole unit being described in the finding aid. What then follows are data elements that describe that whole unit, including a special subset of core data elements that are gathered together under a parent element called Descriptive Identification (DID). These DID subelements are thought to be among the most important for ensuring a good basic description of an archival unit or component. Grouping these elements together serves several purposes. It ensures that the same data elements and structure are available at every level of description within the EAD hierarchy, facilitates the retrieval or other output of a cohesive body of elements for resource discovery and recognition, and, because the elements appear together in the tag library and on software menus and templates, helps to remind encoders to capture descriptive information they may otherwise overlook.

EAD Tag Library Version 1.0