Wikimedia Bugzilla is closed!

1) Bad value X-UA-Compatible for attribute http-equiv on element meta.",

2) link rel="edit" should be an absolute URL. Bad value edit for attribute rel on element link: Not an absolute URL. The string edit is not a registered keyword or absolute URL.

The markup causing these issues is as follows:
<link rel="edit" title="Edit" href="/w/index.php?title=W3CValidationTest&amp;action=edit" />
<meta http-equiv="X-UA-Compatible" content="IE=EDGE" />

These should at the very least be moved out of OutputPage into the skin or be configurable via OutputPage->setProperty. The mobile skin has no need for the X-UA-Compatible meta tag and wishes to use HTML Validation tests as part of its continuous integration testing to catch problems such as unclosed tags.

On a side note: headElement should do with a massive refactor and imo should probably be part of Skin.php so that it can be tweaked where necessary.