diff --git a/core/lib/Drupal/Core/Render/Element/Select.php b/core/lib/Drupal/Core/Render/Element/Select.php
index f78dfa9..3f8615b 100644
--- a/core/lib/Drupal/Core/Render/Element/Select.php
+++ b/core/lib/Drupal/Core/Render/Element/Select.php
@@ -16,6 +16,9 @@
  *   optgroup. Nesting optgroups is not allowed.
  * - #empty_option: The label that will be displayed to denote no selection.
  * - #empty_value: The value of the option that is used to denote no selection.
+ * - #multiple: FALSE if one option can be selected and TRUE if more than one
+ *   options can be selected.
+ * - #size: Specifies the number of visible options.
  *
  * Usage example:
  * @code