fill a rectangle
xfrect(x,y,w,h)
xfrect(rect) // rect =[x,y,w,h]
:x,y,w,h four real values defining the rectangle. :
xrect fills a rectangle defined by [x,y,w,h] (upper-left point, width, height) in user coordinates.
`plot2d`_(0,0,-1,"010"," ",[-2,-2,2,2])
`xset`_("color",5)
xfrect(-1,1,2,2)