def get_modifications(self):
        """Extract INDRA Modification Statements from the BioPAX model.

        To extract Modifications, this method reuses the structure of
        BioPAX Pattern's
        org.biopax.paxtools.pattern.PatternBox.constrolsStateChange pattern
        with additional constraints to specify the type of state change
        occurring (phosphorylation, deubiquitination, etc.).
        """
        for modtype, modclass in modtype_to_modclass.items():
            # TODO: we could possibly try to also extract generic
            # modifications here
            if modtype == 'modification':
                continue
            stmts = self._get_generic_modification(modclass)
            self.statements += stmts