Generate trusses for nodes which are neigbours in space (that is, for nodes which are connected by an isoparametric finite element). Only nodes located on the specified geometry entity will be used.
The generated trusses will get an element_group record with value element_group. So in that element group you can put the properties of the trusses (see group_truss_young etc.).
Typically you can use this option to put easy trusses somewhere in a mesh with isoparametric elements.