Note: I don't understand which component this applies to so I selected 'system', if you know where this issue belongs please change it.
A site name such as 'Jack & Jill' should produce a title tag that looks like
<title>Jack & Jill</title>
But currently renders
<title>Jack & Jill</title>
Which results in a warning when the source code is validated.
Related page: http://drupal.org/node/166930
Comments
Comment #1
grendzy commentedsee #461938: Core should consistently filter_xss_admin() on $site_slogan and check_plain $site_name