To effectively answer your question, I'll provide a list of ways augmented reality (AR) interfaces challenge traditional GUI design principles:

1. Contextual awareness: AR interfaces consider the user's environment and situation.

2. Spatial interactions: AR introduces 3D spatial interactions, unlike traditional 2D GUIs.

3. Camera and sensor inputs: AR uses camera and sensor inputs, unlike traditional GUIs.

4. Overlapping physical and digital spaces: AR blends physical and digital elements.

5. Dynamic environment: AR interfaces adapt to changing environments.

6. User movement and orientation: AR considers user movement and orientation.

7. Focus and attention: AR interfaces guide user focus in a dynamic environment.

8. Information density: AR balances information density with real-world context.

9. Gesture and voice inputs: AR often uses gesture and voice inputs.

10. Feedback and guidance: AR provides feedback and guidance in a dynamic environment.

11. User calibration and training: AR may require user calibration and training.

12. Content creation and management: AR introduces new content creation and management challenges.

By understanding these challenges, GUI designers can develop innovative AR interfaces that effectively merge physical and digital spaces.