if (!/,$/.test(preceedingSubfield.value)) {
                if (!/^[[(]/.test(currentSubfield.value)) {
                    const nextValue = preceedingSubfield.value + ',';
                    debug(`Updated subfield ${preceedingSubfield.code} from '${preceedingSubfield.value}' to '${nextValue}'`);
                    preceedingSubfield.value = nextValue;