def tag_residue_solvent_accessibility(self, tag_type=False, tag_total=False,
                                          force=False, include_hetatms=False):
        """Tags `Residues` wirh relative residue solvent accessibility.

        Notes
        -----
        THIS FUNCTIONALITY REQUIRES NACESS.
        This function tags the Monomer with the *relative* RSA of
        the *whole side chain*, i.e. column 2 of the .rsa file that
        NACCESS writes.

        References
        ----------
        .. [1] Hubbard,S.J. & Thornton, J.M. (1993), 'NACCESS',
           Computer Program, Department of Biochemistry and Molecular
           Biology, University College London.

        Parameters
        ----------
        force : bool, optional
            If `True`, the ta will be run even if `Residues` are
            already tagged.
        tag_type : str, optional
            Specifies the name of the tag. Defaults to
            'residue_solvent_accessibility'. Useful for specifying more
            than one tag, e.g. if the Polymer is part of an Assembly.
        tag_total : bool, optional
            If True then the total rsa of the Polymer will be tagged
            in the 'total accessibility' tag.
        include_hetatms:bool, optional
            If true then NACCESS will run with the -h flag and will
            include heteroatom solvent accessibility where it can.
            Helpful if your file has MSE residues that you don't
            convert to MET, but best check if they are there
            before using the flag.
        """
        if tag_type:
            tag_type = tag_type
        else:
            tag_type = 'residue_solvent_accessibility'
        tagged = [tag_type in x.tags.keys() for x in self._monomers]
        if (not all(tagged)) or force:
            naccess_rsa_list, total = extract_residue_accessibility(run_naccess(
                self.pdb, mode='rsa', path=False,
                include_hetatms=include_hetatms), path=False, get_total=tag_total)
            for monomer, naccess_rsa in zip(self._monomers, naccess_rsa_list):
                monomer.tags[tag_type] = naccess_rsa
            if tag_total:
                self.tags['total_polymer_accessibility'] = total
        return