Most computer languages restrict the functions available to previously defined routines.
In many applications you might find it desirable to change the functions. To use a new function, you might have to recompile your entire program. What you would like is a way of changing a selected function and have the new function used every time the old one is referred to in the already completed part of the program. The function of PAGE is to clear the screen and home the cursor. The code necessary to do this is usually different from one terminal to the next.