TIdSchedulerOfThreadDefault = class(TIdSchedulerOfThread);

TIdSchedulerOfThreadDefault is a TIdSchedulerOfThread descendant that implements the default thread-based scheduler as used in TIdTCPServer and descendant classes. 

TIdSchedulerOfThread introduced a scheduler using threads to represents a task that is managed by the Scheduler for the server. TIdSchedulerOfThreadDefault extends the ancestor class implementing methods that create the yarns and threads needed for the default implementation.