in src/flagutil.js [106:112]
exports.validateVersionString = function (version, opt_allowNonSemver) {
const pattern = opt_allowNonSemver ? /^\d+\.\d+\.\d+(-?rc\d)?$/ : /^\d+\.\d+\.\d+(-rc\d)?$/;
if (!pattern.test(version)) {
apputil.fatal('Versions must be in the form #.#.#-[rc#]');
}
return version;
};