The transferEvidence operation, which is one of the functions on the Evidence Interface, handles the foreign keys on a custom entity when evidence is broadcast from one case to another. For example, if a custom entity has one or more case participant role fields, code needs to exist in this function to manage the foreign keys. This is so these fields on the new record on the target case do not point at case participants on the source case. For evidence generated by the Cúram Evidence Generator, the code for managing the foreign keys will be automatically generated.