Programming by Demonstration (PbD) is a new paradigm for the programming of devices (robots, household appliances, machines) or interactive sofrware (text or graphics editors). The system enables programming without explicit coding. As a prototype of a new PbDsystem, the m r a m m i n g by &monstration Graphics Editor ProDeGE+ with extendable domain theory, is introduced. The prototype illustrates how generalizedfunctions can be generated based on a set of action sequences that are demonstrated in an inferactive system. Additional interactions with users (Dialog-Based Learning) help to reduce the hypothesis space of the PbD system. This can help to ensure that the generatedfunction is the same as the user-intendedfunction. Finally, the new approach enables users to extend the domain theory of the graphics editor using PbD so that they have an opportunity to reduce the limits of the given domain theory while the system is in use.