back to old boundaries

What?

// <!-- reflection at bottom and top boundary -->
function checkY(y,Num){
   height=parseIntohnepx(StyleOfTheSquare[Num].height);
   edge=doc_height-height
   if (y > edge)  {
      y=doc_height-height;
      yspeed[Num]*=-Yreflectionrate; 
      // y=0 + y - doc_height;
   }
   if (y<0) {
      y=0;
      yspeed[Num]*=-Yreflectionrate; 
      // y=doc_height+y;
   }
   return y;
}

How?

What's next??