All this INIT does is patch GetResource to use the CDEF from this file, which is loaded into the System heap at boot time and kept there (so this file doesn't have to be kept open), if the caller requested a resource of resType 'CDEF' and resID 0 and the RomMapInsert is true. All this is so the ‘oi polloi won't have to modify their System files, and so I don't have to write an installer. (I wrote an installer, but you need to run it from another system disk, and then you need to keep it around to de-install, and that's no fun, so you get this instead, inspired by Eric's "MainWDEF".)
You can go ahead and insert this CDEF into the System file if you don't want so many INITs hanging around. Cut, Paste, and renumber it to resID 0.
If you do this, you'll also need to modify the ROv# that corresponds to your ROM. And if you don't know what that means (ROv# resources are described in the Resource Manager supplement in IM IV), you probably shouldn't be playing with it and should go ahead and use this as an INIT.
Think very carefully about what will happen if you want to remove the CDEF from the System file. If it isn't clear, you should run ResEdit from another system disk.
