After a quick W3C validation check, I saw that the charset is not propely defined.

You have to modifiy in template.php this

function skeletontheme_html_head_alter(&$head_elements) {
  $head_elements['system_meta_content_type']['#attributes'] = array(
    'charset' => 'utf-8'
  );
}

to this 

 function skeletontheme_html_head_alter(&$head_elements) {
  $head_elements['system_meta_content_type']['#attributes'] = array( 
  'http-equiv' => 'Content-Type',
    'content' => 'text/html; charset=utf-8',
  );
}

Comments

gtsopour’s picture

gtsopour commented
Assigned: Unassigned » gtsopour
choster’s picture

choster commented

There had been a validator bug back in the day, but that was fixed long ago. Are you sure you're validating against HTML5?

While the long form declaration is still permitted, the short form was invented because the long form is a bit redundant/useless.

Anonymous’s picture

Anonymous (not verified) commented

Making this modification removes 1 Error and 1 Warning during the validation process.

Warning -> No Character encoding declared at document level
Error -> Line 15, Column 17: there is no attribute "charset"

There are 5 other errors;
Line 145, Column 114: required attribute "alt" not specified
Line 145, Column 115: end tag for "img" omitted, but OMITTAG NO was specified
Line 182, Column 98: end tag for "img" omitted, but OMITTAG NO was specified
Line 198, Column 100: end tag for "img" omitted, but OMITTAG NO was specified
Line 211, Column 38: duplicate specification of attribute "class"

SOLUTIONS: all on main page
Edit the "Skeleton is a Responsive, Mobile-Friendly Theme" page;
add -> alt="" / before closure of img ....... ?>/mockup/skeleton_devices.png" alt="" />

Modify Downloads (Featured left) block; Add img closure />

Modify Documentation (Featured right) block Add img closure />

skeleton/sites/all/themes/skeletontheme/templates/page.tpl.php
Change;
div id="footer"
div class="container" class="sixteen columns

to;
div id="footer"
div id="container" class="sixteen columns

Now validates : This document was successfully checked as XHTML + RDFa!

Gary