code: def box(self, x0, y0, width, height):
          
          assert width > 1
          assert height > 1
  
          width -= 1
          height -= 1
  
          for x in range(x0, x0 + width):
              self.point(x, y0, "-")
              self.point(x, y0 + height, "-")
  
          for y in range(y0, y0 + height):
              self.point(x0, y, "|")
              self.point(x0 + width, y, "|")
  
          self.point(x0, y0, "+")
          self.point(x0 + width, y0, "+")
          self.point(x0, y0 + height, "+")
          self.point(x0 + width, y0 + height, "+")
docs: Create a box on ASCII canvas.
  
          Args:
              x0 (int): x coordinate of the box corner.
              y0 (int): y coordinate of the box corner.
              width (int): box width.
              height (int): box height.