@ ... Box, @ ... To, @ ... Clear, @ ... Fill

These @ commands all relate to drawing on a window. @ ... BOX and @ ... TO draw boxes, @ ... CLEAR clears a rectangular area (sort of the inverse of drawing a box, we guess) and @ ... FILL fills a rectangular area with color. There's no reason to use these commands ever. Use Visual FoxPro's controls and drawing methods instead. They're more powerful and better behaved.