<?php
if ( function_exists('register_sidebars') )
    register_sidebars(2);

function tj_comment_class( $classname='' ) {
	global $comment, $post;

	$c = array();	
	if ($classname)
		$c[] = $classname;

	// Collects the comment type (comment, trackback),
	$c[] = $comment->comment_type;

	// If the comment author has an id (registered), then print the log in name
	if ( $comment->user_id > 0 ) {
		$user = get_userdata($comment->user_id);

		// For all registered users, 'byuser'; to specificy the registered user, 'commentauthor+[log in name]'
		$c[] = "byuser comment-author-" . sanitize_title_with_dashes(strtolower($user->user_login));
		// For comment authors who are the author of the post
		if ( $comment->user_id === $post->post_author )
			$c[] = 'bypostauthor';
	}

	// Separates classes with a single space, collates classes for comment LI
	return join(' ', apply_filters('comment_class', $c));
}

?>