The index corresponds to a node. The node is assumed to be located on the boundary of the domain if this record is specified. You can set switch is set to -yes.
For the options control_mesh_remesh, control_new_mesh and the contact algorithm it is necessary to give all the nodes on the boundary.
These node_boundary records can also be referred to by geometry_set records.
It is not allowed to give all nodes of one element node_boundary records.