The Glossary entry print view uses the tag <p align="center"> and the align attribute is not valid in XHTML 1.0 Strict

Instead of
<p align="center">
we should use
<p style="text-align: center">

This is done by modify the file: /moodle/mod/glossary/print.php
We should change the line:
echo "<p align=\"center\"><strong>".clean_text($pivottoshow)."</strong></p>" ;
for
echo "<p style=\"text-align: center\"><strong>".clean_text($pivottoshow)."</strong></p>" ;