How can HTML code validation impact the functionality of PHP scripts?

When HTML code is not properly validated, it can lead to errors in the PHP scripts that interact with it. This can cause unexpected behavior, such as incorrect data being passed between the HTML and PHP components. To ensure smooth functionality, it is important to validate the HTML code to prevent any issues that may arise.

<?php
// Validate HTML code before interacting with it in PHP
$html = "<p>Hello, world!</p>";
$validated_html = htmlspecialchars($html, ENT_QUOTES, 'UTF-8');
echo $validated_html;
?>