code: func (h *windowsAnsiEventHandler) effectiveSr(window SMALL_RECT) scrollRegion {
  	top := addInRange(window.Top, h.sr.top, window.Top, window.Bottom)
  	bottom := addInRange(window.Top, h.sr.bottom, window.Top, window.Bottom)
  	if top >= bottom {
  		top = window.Top
  		bottom = window.Bottom
  	}
  	return scrollRegion{top: top, bottom: bottom}
  }
docs: // effectiveSr gets the current effective scroll region in buffer coordinates