Selecting the intersection of two lines

I’m creating a geometric proof diagram and I need to be able to draw a line starting at the intersection of two arbitrary lines (where the intersection is not on a grid point). How do I place a magnet specifically at the intersection of two lines (or select that intersection to start a line?). Inkscape has a sophisticated snap palette which allows snapping to intersections, wondering if this capability can be achieved in OmniGraffle somehow?