Field definition and scope:

Fields 790-799 are reserved for local added entry use and local definition.  For instance, an institution could use the fields for added entries for variant forms or former names of the name found in the 1XX Primary Name field.  For interchange purposes, documentation of the structure of the 79X fields and input conventions should be provided to exchange partners by the organization initiating the exchange.

See also:

7XX  Added Entries

Variable Data Fields