The AppDomainManager provides the host with a mechanism to bootstrap into managed code and to control the creation and settings of each AppDomain. The AppDomainManager is loaded into each AppDomain when that AppDomain is created. If it chooses, the CLR notifies the host that the application domain has been created by setting the value of the pUnkAppDomainManager parameter.
In its implementation of the SetAppDomainManager method, the host can set the assembly name and type for the application domain manager.