CLS - a  device I/O statement that clears the display screen
 
Syntax
  CLS [{0|1|2}]
    - If all arguments are omitted, either the graphics viewport or the text
      viewport are cleared, depending upon previous uses of VIEW statement.
    - 0 clears the screen of all text and graphics.
    - 1 clears only the graphics viewport, if it is active.
    - 2 clears only the text viewport, leaving bottom screen line unchanged.
 
See Also  <VIEW> - to see how to activate the graphics viewport
          <VIEW PRINT> - to see how to set the text viewport
          <WINDOW> - to see how to customize the graphics viewport