The grammar version of the connection device
The advantage is that changes that the user makes in the initial slopepositions are propagated all the way through to the branches based on the control and surface geometry.
I choose to program a surface spanning to two guidelines using additional lines as handles to deform the resulting surface. The surface is based on cubic splines which connect the staring and the ending slope of the respective points.

For the left demonstration type demo at the command line, or press the demo button

There are three commands available:

1. 3dspline
which prompts the user to pick four points, the points to be connected and the slopepoints. options are the number of points the spline is drawn in and the amount of tension on the spline.

2. Mesh
which prompts the user to pick to existing lines as borders of the surface and two existing lines as handles to determine the starting and ending slope. There are only splines in one direction.(u-direction) option are the amount of cells in u and v irection and again the tension of the splines.

3. Crossmesh
which prompts the user to pick two existing lines as borders of the surface and then four handles one each for a side of the surface. The picking order has to follow the above order in order to acchieve desired results