What are the best practices for filtering out unwanted HTML elements and attributes in PHP when using an editor like CKEditor?

When using a rich text editor like CKEditor in PHP, it is important to filter out unwanted HTML elements and attributes to prevent potential security vulnerabilities and maintain the integrity of the content. One way to achieve this is by using a library like HTML Purifier, which allows you to define a whitelist of allowed elements and attributes while stripping out any disallowed content.

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

// Configuration settings for HTML Purifier
$config = HTMLPurifier_Config::createDefault();
$config->set('HTML.Allowed', 'p,b,a[href],i,u');

// Create HTML Purifier instance
$purifier = new HTMLPurifier($config);

// Cleanse the input HTML content
$cleanHtml = $purifier->purify($_POST['editor_content']);

// Output the sanitized HTML content
echo $cleanHtml;