tring(label, var_args) {
            const varArgs = arguments;
            return label.replace(/\$(.|$|\n)/g, function(m) {
                assert(m.match(/\$[$1-9]/), 'Unescaped $ found in localized string.');
                return m === '$$' ? '$' : varArgs[m[1]];
            });
        }

        /**
   * Returns a formatted string where $1 to $9 are replaced by the second to
   * tenth argument, split apart into a list of pieces describing how the
   * substitution was performed. Any standalone $ si