The Extent element is essentially the physical description area, used to describe the physical nature of textual and non-textual materials. It is measured in metres or centimetres for textual records and either as exact or estimated numbers for photographs, maps, etc. The Extent element should say how many units there are and of what. For example:
Extent: 50 m. of textual records.
Extent: ca. 200 photographs.
When listing more than one type of record in the same element, either separate each one with a ". --" or start a new paragraph for each. For example:
