diff --git a/core/lib/Drupal/Core/Render/Element/Select.php b/core/lib/Drupal/Core/Render/Element/Select.php
index f78dfa9..1435b99 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: A Boolean indicating either single or multiple values can be
+ *   selected.
+ * - #size: The width of the field (in characters).
  *
  * Usage example:
  * @code