Changes the current component selection to select only the components that form a boundary around the current component selection. The previously selected interior components that are not part of the boundary are unselected.

For example, if you have a polygon mesh comprised of four-sided polygons (quads) with nine interior vertices selected, in the shape of a square grid, and then choose Select > Select Selection Region, the eight vertices that form the boundary on the selection remain selected on the mesh. The interior vertex is unselected.