This routine contains a loop over all edges. For each edge i which is to be divided into two sub-edges the following actions are taken:
After leaving newnodes a random contribution is added to the coordinates of each new node while moving them towards the center of gravity of their base element (=perturbation of the nodal position from a surface position to a subsurface position). This ensures that each new node lies within a tetrahedral element and not on its faces or edges. This facilitates the insertion of the new nodes in the existing mesh and is particularly important for the newly created external surface nodes. Indeed, the insertion procedure explained in  works only for nodes not lying on the external surface. The insertion of the new nodes is done one by one after reordering them in an aleatoric way.