A User Defined Domain Model is a domain message model defined by a party other than LSEG. These may be defined to solve a specific user or system need in a particular deployment which is not resolvable through the use of a Domain Model. Any user-defined model must use a domain value between 128 and 255. If needed, domain model designers can work with LSEG to define their models as standard Domain Models. This allows for the most seamless interoperability with future Domain Model definitions and with other LSEG products.