This reads a set of parameters from file, which should act on the atom classes previously defined. Any parameters read are added to any already in this object (to clear them all, simply create a new object). The format of the group restraints file is the same as the MODELLER restraints format (see Section 5.3.1) except that rather than numeric atom indices, atom group names (as defined in the classes file) are used. These restraints are further limited, in that they can act only on 1 or 2 atoms.