Issue #405360 by Liam Morland, mgifford, Everett Zufelt: Added Use...

Issue #405360 by Liam Morland, mgifford, Everett Zufelt: Added Use aria-describedby to link form elements with form element descriptions.

core/includes/form.inc

@@ -1779,6 +1779,12 @@ function form_builder($form_id, &$element, &$form_state) {
   if (!isset($element['#id'])) {
     $element['#id'] = drupal_html_id('edit-' . implode('-', $element['#parents']));
   }
+
+  // Add the aria-describedby attribute to associate the form control with its
+  // description.
+  if (!empty($element['#description'])) {
+    $element['#attributes']['aria-describedby'] = $element['#id'] . '--description';
+  }
   // Handle input elements.
   if (!empty($element['#input'])) {
     _form_builder_handle_input_element($form_id, $element, $form_state);
@@ -4186,7 +4192,11 @@ function theme_form_element($variables) {
   }
 
   if (!empty($element['#description'])) {
-    $output .= '<div class="description">' . $element['#description'] . "</div>\n";
+    $attributes = array('class' => 'description');
+    if (!empty($element['#id'])) {
+      $attributes['id'] = $element['#id'] . '--description';
+    }
+    $output .= '<div' . drupal_attributes($attributes) . '>' . $element['#description'] . "</div>\n";
   }
 
   $output .= "</div>\n";