What are the best practices for structuring PHP and HTML code to ensure validation?

To ensure validation in PHP and HTML code, it is best practice to separate the presentation layer (HTML) from the logic layer (PHP). This can be achieved by using a template engine like Twig or Smarty to keep the HTML code clean and separate from the PHP logic. Additionally, input validation should be performed on the server side using PHP to prevent any malicious input from being processed.

<?php
// Validate input data
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = htmlspecialchars($_POST["name"]);
    $email = filter_var($_POST["email"], FILTER_VALIDATE_EMAIL);
    
    // Perform additional validation as needed
    
    // Process the data
    // ...
}
?>