Add missing 'class' comments

404.php

@@ -14,7 +14,7 @@ get_header(); ?>
 			<article id="post-0" class="post error404 not-found">
 				<header class="entry-header">
 					<h1 class="entry-title"><?php _e( 'Oops! That page can&rsquo;t be found.', '_s' ); ?></h1>
-				</header>
+				</header><!-- .entry-header -->
 
 				<div class="entry-content">
 					<p><?php _e( 'It looks like nothing was found at this location. Maybe try one of the links below or a search?', '_s' ); ?></p>
@@ -28,7 +28,7 @@ get_header(); ?>
 						<ul>
 						<?php wp_list_categories( array( 'orderby' => 'count', 'order' => 'DESC', 'show_count' => 1, 'title_li' => '', 'number' => 10 ) ); ?>
 						</ul>
-					</div>
+					</div><!-- .widget -->
 
 					<?php
 					/* translators: %1$s: smilie */
@@ -39,7 +39,7 @@ get_header(); ?>
 					<?php the_widget( 'WP_Widget_Tag_Cloud' ); ?>
 
 				</div><!-- .entry-content -->
-			</article><!-- #post-0 -->
+			</article><!-- #post-0 .post .error404 .not-found -->
 
 		</div><!-- #content -->
 	</div><!-- #primary .site-content -->