In fairness, the author does make note of that: Note - In a real-world application, validating an email address using a regular expression is not enough for ma

In fairness, the author does make note of that: Note - In a real-world application, validating an email address using a regular expression is not enough for many situations, such as when a user signs up. Once you have confirmed that the input text is an email address, you should always follow through with the standard practice of sending a confirmation/activation email.