Chapter 13. Form Validation
In this lesson you will learn some techniques for validating form input in a user-friendly way.
The principles of validating user-submitted input are fairly straightforward: Just check each item in $_POST in turn and make sure it matches a set of criteria. However, making sure the user is able to correct any mistakes and resubmit the form with a minimum of fuss presents a bit more of a challenge.
Enforcing Required Fields
The most basic type of form validation is to enforce that a particular field must contain a value. In the case of a text input that is submitted with no value entered, the element in $_POST is still created, but it contains an empty value. Therefore, you cannot use isset to check whether a value was ...
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