Issue #678594 by linclark, mlncn, kathyh: Fix RDFa markup for file/image formatters.

core/modules/rdf/rdf.module

@@ -781,6 +781,9 @@ function rdf_field_attach_view_alter(&$output, $context) {
  * Implements MODULE_preprocess_HOOK().
  */
 function rdf_preprocess_image(&$variables) {
+  // Adds the RDF type for image.  We cannot use the usual entity-based mapping
+  // to get 'foaf:Image' because image does not have its own entity type or
+  // bundle.
   $variables['attributes']['typeof'] = array('foaf:Image');
 }