Resource Attributes(IM:XP)

Inside Macintosh: QuickDraw GX Printing Extensions and Drivers /: Chapter 6 - Printing Resources / About the Printing Resources

Resource Attributes
All of the resources that you define for your printing extensions and printer drivers need to be loaded into the system heap and need to be purgeable. System resources are stored in the system heap as opposed to the application heap, where application resources are stored. Purgeable resources can be purged by the Memory Manager when space is required, as described in Inside Macintosh: Memory.
You need to specify these attributes in the first line of every resource that you define for your extensions and drivers, as in this example:
resource gxOverrideType (gxPrintingDriverBaseID+1, sysHeap,
                                                   purgeable)
{
};
resource statusType (kDriverStatus, sysHeap, purgeable)
{
};
WARNING
You need to store your resources in the system heap to allow the memory that they use to be shared when multiple copies of your driver are active at the same time. You must, however, take care to not release a resource that is in use by another copy of your driver.