cls [line | page]
cls resets the current window's clipping region to encompass the entire window, clears the entire contents of the window to the background pattern and color (usually white), and resets the pen to a position near the upper-left corner (0, 0) of the window.
cls line clears a rectangle as high as the current font, from the current pen position to the right side of the window. This is handy for clearing text from the current line only. The pen position is not affected.
cls page clears the text from the pen position to the right side of the window (as
cls line does), then clears the entire window below the pen position. The pen position is not affected.