Allow More HTML Tags in WordPress Comments

WordPress allows a select few HTML tags within the content of post comments.  This is an awesome feature, of course, because it prevents XSS security holes and other malicious code from being injected by spammers, hackers, and jerks.  Unfortunately there are many other tags that bloggers may want to support;  for example, tech bloggers may want to support PRE tags so commenters can post code.  Luckily it's quite easy to allow more tags within your WordPress comments:

// Create function which allows more tags within comments
function allow_pres() {
 global $allowedtags;
 $allowedtags['pre'] = array('class'=>array());
}

// Add WordPress hook to use the function
add_action('comment_post', 'allow_pres');

The global $allowedtags variable holds an array of allowed comment tags, so adding the pre key will allow PRE elements within comments.  The class key within the pre array allows the class attribute for any PRE tags posted within the comment, so not only can you allow additional HTML tags, but you can also specify allowed attributes too!  This function is added to the comment_post hook (same hook that AJAX comments use) so as to only add desired tags when a comment is posted.