[CONNECT C++] Relationships

The MicroStationAPI document says this about Relationships: A relationship handler major ID must be a value allocated from the XAttributeHandlerMajorIDs value space. Edit msdefs.h to allocate an XAttributeHandlerMajorID.

However, file msdefs.h does not exist in the SDK (Update 11).   Plus, I don't like the recommendation to edit a delivered header file, especially when that is a file that does not exist.  How does one obtain an XAttributeHandlerMajorID?