...
The plug-in name is needed to distinguish between callbacks registered by different plug-ins. This is a string you provide when you register the callback, so it's recommended (but not enforced) to use the name of your plug-in here. The type field is a numeric value corresponding to the MaxwellMayaAPI::ExportCallbackType enum. You should only have one callback of each type for a given plug-in name. The language field is an integer corresponding to the MaxwellMayaAPI::ExportCallbackLanguage enum and specifies if the callback command is MEL or Python. The final field is the command string which is executed by the Maxwell plug-in.
Managing this variable correctly can be tedious, so MaxwellMayaAPI provides a few static inline methods for it: SetExportCallback(), RemoveExportCallback() and RemoveExportCallbacks(). These can be called without loading the API. If you do not need these methods and do not want them declared, you can define the MAXWELL_MAYA_NO_CALLBACK_HELPERS macro before including MaxwellMayaAPI.h.
...