Jan Vroonhof <vroonhof(a)math.ethz.ch&gt; writes: Because it covers the whole window, including the clipped line. With the GUARANTEE value, I need to apply (forward-line) twice to the value I get. But I could live with either, it's not that important. Consistency is, though. One of the basic postulates of our redisplay mechanism is that scrolling is tightly integrated with redisplay. Chuck Thompson put it like this: The traditional scrolling code in Emacs breaks in a variable height world. It depends on the key assumption that the number of lines that can be displayed at any given time is fixed. This led to a complete separation of the scrolling code from the redisplay code. In order to fully support variable height lines, the scrolling code must actually be tightly integrated with redisplay. Only redisplay can determine how many lines will be displayed on a screen for any given starting point. And so on. I admit I fail to understand your explanation. Looking at the code, it seems that window-end employs the line-start cache in the GUARANTEE case, while window-start always returns the stored value. I have no idea if it is feasible to use the line-start cache for the purposes of window-start. It may be hard or impossible. It may also be that the implementor of GUARANTEE simply forgot about window-start, or that he didn't feel like doing it at the time. (To my dismay, the change to window-end is not mentioned in the ChangeLog. Neither is it documented in Lispref.)