Enables definition of text window, i.e. area of screen to which future text is written (rather than being written anywhere on the screen).
VDU 28,lx;by;rx;ty;
| lx | Left X |
| by | Bottom Y |
| rx | Right X |
| ty | Top Y |
Four coordinates are given as character positions, with the origin being 0,0 at the top left of the screen. Maximum values depend on the current screen mode.