tk appname ?newName?
If newName isn't specified, this command returns the name of the application (the name that may be used in send commands to communicate with the application). If newName is specified, then the name of the application is changed to newName. If the given name is already in use, then a suffix of the form "#2" or "#3" is appended in order to make the name unique. The command's result is the name actually chosen. newName should not start with a capital letter. This will interfere with option processing, since names starting with capitals are assumed to be classes; as a result, Tk may not be able to find some options for the application. If sends have been disabled by deleting the send command, this command will reenable them and recreate the send command.
Is there an effective way to ask the window manager what appnames it knows? This is an issue for send consumers, of course.