• FIX has been introducing a number of new repeating groups in the context of MiFID II. Questions have been raised as to how they can be supported as part of FIX 4.2.
• The official policy for supported legacy versions (FIX 4.2, FIX 4.4, FIX 5.0 SP2) is to directly use tags, components or repeating groups from latest Extension Pack. Legacy versions are not extended on the application level and only changed in case of errors (aka Errata version).
• A Technical Addendum has been issued to change the timestamp datatype for supported legacy versions due to the regulatory requirement to support microsecond precision. Please see https://www.fixtrading.org/packages/time-precision-technical-addendum/ for details.
• Repeating groups were already part of FIX 4.2 (e.g. allocation group: tags 78=NoAllocs, 79=AllocAccount, 80=AllocShares) even though some users chose not to implement them. Please refer to FIX 4.2 Specification with Errata 20010501, page 9, section “Repeating Groups:”.
• FIX provides user-defined fields in the range 8000-8499 for “flat” versions of selected repeating groups and only in the context of regulatory requirements (e.g. 8013=TrdRegPublicationReasons (plural) with space delimited values to emulate 2670=TrdRegPublicationReason (singular) as part of a repeating group). This 8000-8499 range of user-defined fields are under FIX Global Technical Committee’s management.
• “Flat” versions cannot be provided for complex repeating groups such as Parties, i.e. repeating groups with multiple fields or nested repeating groups.
• A huge amount of functionality added over the last 10 years is covered by FIX with the help of (nested) repeating groups. It is well worth the effort to invest into the capability of supporting repeating groups to take advantage of them natively.