Here's an example... taskerr is using deprecated/obsolete HTML, which will likely be a negative
SEO ranking signal. Also heading flow is broken (syntax invalid), likely because of this too...
http://validator.w3.org/check?uri=ht...Inline&group=0
Pages should validate like this...
http://validator.w3.org/check?uri=da...Inline&group=0
With two warnings.
1) one for using HTML5 (best
SEO signal)
2) one for passing charset via Apache instead of at document level, which is required to speed up IE rendering
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Vantage is even worse, with 40 errors + 18 warnings...
http://validator.w3.org/check?uri=http%3A%2F%2Fdemos.appthemes.com%2Fvanta ge&charset=%28detect+automatically%29&doctype=Inli ne&group=0
Because your themes use <hgroup> (deprecated) instead of <header> is part of the reason.
Another problem is your themes break semantic structure, meaning tags placed which break the the HTML spec...
Like <div> tags inside <hgroup> which is incorrect syntax.
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Jobroller is 19 errors + 10 warnings...
http://validator.w3.org/check?uri=http%3A%2F%2Fdemos.appthemes.com%2Fjobro ller%2F&charset=%28detect+automatically%29&doctype =Inline&group=0
In short, probably best to add an item to your release process to run all parent themes + child themes + plugins (that generate HTML) through the W3C validator to ensure clean code before release.
Also best to turn on full
WP debug + ensure there are no
WP errors... by adding this to your
wp-config.php file...
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors', 0);
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These are all things that smart clients look at when vetting code to run on high traffic sites.