template_preprocess_forum_topic_list in drupal-7.x/modules/forum/forum.module

Preprocesses variables for forum-topic-list.tpl.php.

<?php

/**
 * @file
 * Displays an appropriate icon for a forum post.
 *
 * Available variables:
 * - $new_posts: Indicates whether or not the topic contains new posts.
 * - $icon_class: The icon to display. May be one of 'hot', 'hot-new', 'new',
 *   'default', 'closed', or 'sticky'.
 * - $first_new: Indicates whether this is the first topic with new posts.
 *
 * @see template_preprocess_forum_icon()
 * @see theme_forum_icon()
 *
 * @ingroup themeable
 */
?>
<div class="topic-status-<?php print $icon_class ?>" title="<?php print $icon_title ?>">
<?php if ($first_new): ?>
  <a id="new"></a>
<?php endif; ?>

  <span class="element-invisible"><?php print $icon_title ?></span>

</div>