The MLC standard allows to communicate, for contributors to sound recordings and music videos a role and, where appropriate, information about the instrument or instrument(s) played. 

This article discusses MLC 1.3.x. The issue described herein has been fixed in MLC 1.4.

This can be communicated in, for example, the InstrumentType element of the FeaturedArtist composite. DDEX has, over the last few years collated a large list of instruments that can be used within this tag. 

However, the XML Schema Definitions for MLC 1.3 and 1.3.1 has a bug in that the InstrumentType element is not limited to this allowed value set. 

Implementers are requested to use instruments from the list used in MLC 1.4. It is available from the Data Dictionary for MLC 1.4. If – and only if – an instrument that is not included in the above list, should the message sender should simply use its own value.