i guess your questions is the coupling options. tangancy means that If the sections have the same number of tangency discontinuity points, these points are coupled together between sections while Tangency then curvature means If the sections have the same number of tangency and curvature
discontinuity points, tangency discontinuity points are coupled
together between sections, then curvature discontinuity points are
coupled together between sections.
refer to this page if you need more help: http://www.training.engineering.com/solo/onlineobjects/15257 /content/