Thanks for responses. So opinion remains divided? As a new subscriber to this list I am unable to evaluate the different responses with any confidence.

In the Outline of elements and attributes (3.3) page is the statement:

All top-level elements and all attributes are optional, but you must have at least one element. Subelements are optional, although in some cases you may not have empty containers.

In the MODS User Guidelines (3) page several top level elements are described as "wrapper" elements but "location" is not so described.

On the same site it is stated:

Mandatory elements. No element is mandatory in a MODS record, however, every MODS record requires at least one element. Applications may wish to develop profiles specifying mandatory elements as needed.

If it is illegal to use "location" unless it contains a subelement, how should one interpret the above statements?

Many thanks again for your help.