It is best illustrated by an example from the BriefFamily.
In Brief, the first press of the HOME key takes the cursor to the "home" of the line (i.e. the first column). A subsequent press of the HOME key takes the cursor to the "home" of the page (i.e. coordinate (1,1) ). Yet another press will take the cursor to the HOME of the file (ie. absolute (1,1) ). The END key works in an analogous fashion in Brief.
This is very handy from a users standpoint. It is analogous to the multiple clicks in a GUI such as MS Windows/XP, where each click broadens the scope of the Selection.