Adds widget area to 404 template

404.php

@@ -14,11 +14,21 @@
 				<div class="main-content content-main">
 
 					<article id="post-0" class="post error404 no-results not-found">
-						<header class="entry-header">
-							<h1 class="entry-title">This file was not found.</h1>
-						</header>
 
-						<?php get_template_part( 'inc/site-search' ); ?>
+						<?php if ( is_active_sidebar( 'sidebar-404' ) ) { ?>
+
+							<div id="sidebar-404" class="widget-area" role="complementary">
+								<?php dynamic_sidebar( 'sidebar-404' ); ?>
+							</div>
+
+						<?php } else { ?>
+
+							<header class="entry-header">
+								<h1 class="entry-title">The requested content was not found.</h1>
+							</header>
+							<?php get_template_part( 'inc/site-search' ); ?>
+
+						<?php } ?>
 
 					</article><!-- #post-0 -->
 

functions.php

@@ -324,6 +324,17 @@ function mitlib_widgets_init() {
 		'after_title' => '</h3>',
 		'class' => '',
 	) );
+
+	register_sidebar( array(
+		'name'          => __( 'Migrated Content Notice', 'twentytwelve' ),
+		'id'            => 'sidebar-404',
+		'description'   => __( 'Appears on the 404 page, allowing individual sites to post notices about migrated content', 'twentytwelve' ),
+		'before_widget' => '<aside id="%1$s" class="widget %2$s" role="complementary">',
+		'after_widget'  => '</aside>',
+		'before_title'  => '<h2 class="widget-title">',
+		'after_title'   => '</h2>',
+	) );
+
 }
 add_action( 'widgets_init', 'mitlib_widgets_init' );