A message type that is contained in another message type. In some cases, only part of a message type (for example, only the mandatory fields) is nested, but this "partial" nested message type is also considered to be nested. For example, SWIFT MT 195 could be used to request information about a SWIFT MT 100 (customer transfer). The SWIFT MT 100 (or at least its mandatory fields) is then nested in SWIFT MT 195.