function preview_theme_ob_filter_callback( $matches ) {
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if ( strpos($matches[4], 'onclick') !== false )
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$matches[4] = preg_replace('#onclick=([\'"]).*?(?<!\\\)\\1#i', '', $matches[4]); //Strip out any onclicks from rest of <a>. (?<!\\\) means to ignore the '" if it's escaped by \ to prevent breaking mid-attribute.