This variable identifies the routine to be used as the sub interface routine within a DLL. It applies only to Windows systems. Set DLL_SUB_INTERFACE to the name of the routine you want to use. This name may be sub or any name you choose. The runtime checks DLL_SUB_INTERFACE when a DLL is loaded. You may change its value afterwards without any effect on DLLs that have already been loaded.
If DLL_SUB_INTERFACE is empty (default), the runtime does not look for a sub interface routine in a called DLL.