Leaf has a code error common in themes converted from Drupal 5.

This Leaf is 6.x-1.2 from 2008-Dec-26, a 222.96 KB download.

The code error produces the following error message.
recoverable fatal error: Object of class stdClass could not be converted to string in /home/example/public_html/sites/all/themes/leaf/page.tpl.php on line 3.

The faulty line is shown next.
<html xmlns="http://www.w3.org/1999/xhtml" lang="<?php print $language ?>" xml:lang="<?php print $language ?>">

The following line is the corrected line.
<html xmlns="http://www.w3.org/1999/xhtml" lang="<?php print $language->language; ?>" xml:lang="<?php print $language->language; ?>">

This page uses the corrected page.tpl.php. You can download a zipped copy of the page.tpl.php file fro 6.x-1.2.

After you apply the correction, this page validates as XHTML 1.0 Strict at both W3C and TV.