How do I build polygon regions in ds9?

1. Select "polygon" from the "Region → Shape" menu.
2. Click and drag to draw a box on the image.
3. Select the box and double squares will appear at the corners.
4. The outer set of corner squares indicate that the standard region functions are active:
   • Delete region: use <DELETE> key
   • Move region: use left mouse button (symbol: cross)
   • Resize region: use left mouse button (symbol: box + arrows)
5. The inner set of corner squares allow you to add vertices to the shape:
   • Place cursor on any line segment at desired vertex location
   • Click left mouse button to create the vertex
   • Move vertex with left mouse button (symbol: box within box)