code: func (w *Window) getCell(x, y int) *Cell {
  	pos := x + (y * w.x)
  	if pos < len(w.backingStore) {
  		return &w.backingStore[pos]
  	}
  	return nil
  }
docs: // getCell returns the content of the window cell at the x and y coordinate.
  // getCell shall be called from queue context.