Within an affiliation element (<aff>), the name of an institution may just be given as text, or the institution may be tagged explicitly (as an <institution>) and an institutional identifier recorded (<institution-id>). The element <institution-wrap> collects together both the name of the institution and its identifier.

A single institution may have multiple identifiers, either because different assigning agencies have defined an identifier or because the entity belongs to more than one larger organizational unit, for example, a laboratory may be part of multiple institutions.