FIX validation error: The attribute 'about' may not appear in tag 'div'

The function template_preprocess_entity() of the module Entity API may add an invalid attribute "about" (i.e. for field-collections if the core rdf module is enabled).

This could be easily fixed in the via template_preprocess_entity(), like:

/**
 *  Implements template_preprocess_entity().
 */
function amp_preprocess_entity(&$variables) {
  if (!isset($variables['view_mode']) || 'amp' != $variables['view_mode']) {
    return;
  }

  // Unset unallowed attributes about, set by template_preprocess_entity().
  if (isset($variables['attributes_array']['about'])) {
    unset($variables['attributes_array']['about']);
  }
  if (isset($variables['attributes_array']['typeof'])) {
    unset($variables['attributes_array']['typeof']);
  }
}

This could be done in the custom theme or by this module.