1. A debugging data processing system configured for selectable data on file viewing, the system comprising: a host computing system comprising at least one computer with memory and at least one processor; fixed storage coupled to the host computing system and storing both a target application and also a file containing data written by way of directives of the target application; a debugger executing in the memory of the host computing system and debugging the target application; and, a selectable data on file viewing module coupled to the debugger, the module comprising program code enabled upon execution in the memory of the host computing system to specify the file in a user interface of the debugger, to determine whether to view data in the file from a perspective of the host computing system or the target application, to load the data in the file directly from the fixed storage externally to the target application in response to determining to view the data in the file from the perspective of the host computing system, but otherwise loading the data in the file from the fixed storage through operations performed by the debugger on behalf of the target application in response to determining to view the data in the file from the perspective of the target application, and to display the loaded data in a file viewer of the user interface of the debugger.