I am the author of the Voronoi library. The implementation generates Voronoi diagram for the whole infinite 2D plane. The clipping functionality is not part of the library as it's too ambiguous. Could you explain your usage case in more details?
The better way to clarify any questions related to the Voronoi functionality is to write to boost@lists.boost.org with an email title prefixed with "[Polygon]" or "[Voronoi]".