function pattern(rule, value, source, errors, options) {
  if (rule.pattern) {
    if (rule.pattern instanceof RegExp) {
      if (!rule.pattern.test(value)) {
        errors.push(__WEBPACK_IMPORTED_MODULE_0__util__["e" /* format */](options.messages.pattern.mismatch, rule.fullField, value, rule.pattern));
      }
    } else if (typeof rule.pattern === 'string') {
      var _pattern = new RegExp(rule.pattern);
      if (!_pattern.test(value)) {
        errors.push(__WEBPACK_IMPORTED_MODULE_0__util__["e" /* format */](options.messages.pattern.mismatch, rule.fullField, value, rule.pattern));
      }
    }
  }
}
Rule for validating a regular expression pattern.

 @param rule The validation rule.
 @param value The value of the field on the source object.
 @param source The source object being validated.
 @param errors An array of errors that this rule may add
 validation errors to.
 @param options The validation options.
 @param options.messages The validation messages.