This field was intended for a project to introduce foreign ID functionality into our database. The project was cancelled and we do not have any current plans to resurrect it in the near future.  When a membership is created, this field is automatically populated with 'SS' for individual memberships and 'TI' for organizational memberships.  This mirrors the MASTYP field, which stores 'MI' for individuals and 'MO' for organizations and is used throughout the system.  The IDCODE field is not used by any function and cannot be maintained.