if (empty($_POST["name"])) { $validation->add_error("Name is required"); }In this example, if the user does not fill out the name field in the web form, the validation system will trigger the `add_error` function and display the message "Name is required" to the user. Package library: The `add_error` function is commonly used in various PHP validation libraries such as Laravel Validation, Symfony Validation, and CakePHP Validation.