What are best practices for validating and optimizing HTML output in PHP applications before implementing JavaScript functionality?

When working with PHP applications that output HTML, it is important to ensure that the HTML is valid and optimized before implementing JavaScript functionality. This can help prevent issues with rendering and improve overall performance. One way to achieve this is by using PHP libraries such as HTML Purifier to sanitize and validate the HTML output.

// Include the HTML Purifier library
require_once 'path/to/htmlpurifier/library/HTMLPurifier.auto.php';

// Create a new HTMLPurifier instance
$config = HTMLPurifier_Config::createDefault();
$purifier = new HTMLPurifier($config);

// Sanitize and validate the HTML output
$cleanHtml = $purifier->purify($htmlOutput);

// Output the sanitized HTML
echo $cleanHtml;