You can define part of an underlay that you want to display and plot by setting up a clipping boundary with DGNCLIP, DWFCLIP, PDFCLIP, DGNCLIP, IMAGECLIP, VPCLIP, and XCLIP. The clipping boundary can be a closed polyline, rectangle or a polygon with vertices within the overall extents of the underlay. Each instance of an underlay can only have one clipped boundary. Multiple instances of the same underlay can have different boundaries.
When the clipping boundary is no longer needed, you can delete the clipped boundary from the underlay and the underlay is displayed with its original boundary. You can also invert the area to be hidden inside or outside the clipping boundary. With grips located at the midpoint on the first edge of the clipping boundary, you can invert the display of the clipped reference inside or outside the boundary.