How does the current HTML version (HTML 5) impact the usage of the action attribute in PHP forms?

HTML 5 introduced stricter validation rules for the action attribute in forms. This means that the value of the action attribute must be a valid URL. To ensure compatibility with HTML 5, you should use PHP to dynamically generate the URL for the form action attribute.

<form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>" method="post">
  <!-- form fields here -->
</form>