This example demonstrates that 3-dimensional line force elements (here: Modelica.Mechanics.MultiBody.Forces.Spring elements) can be connected together in series without having a body with mass at the connection point (as usually required by multi-body programs). This is advantageous since stiff systems can be avoided, say, due to a stiff spring and a small mass at the connection point.
For a more thorough explanation, see MultiBody.UsersGuide.Tutorial.ConnectionOfLineForces.