What are some potential security risks when using DHTML with PHP on servers?

One potential security risk when using DHTML with PHP on servers is Cross-Site Scripting (XSS) attacks, where malicious scripts are injected into a web page. To prevent this, it is important to sanitize user input and escape output to ensure that any user-provided data is not executed as code.

// Sanitize user input to prevent XSS attacks
$user_input = htmlspecialchars($_POST['user_input']);

// Output the sanitized user input
echo $user_input;