GLUT implementations should be careful to not limit the conditions under which GLUT routines may be called. GLUT implementations are expected to be resilient when GLUT programs call GLUT routines with defined behavior at ``unexpected'' times. For example, a program should be permitted to destroy the current window from within a display callback (assuming the user does not then call GLUT routines requiring a current window). This means after dispatching callbacks, a GLUT implementation should be ``defensive'' about how the program might have used manipulated GLUT state during the callback.