--- /dev/null
+<?php
+
+namespace Drupal\Core\Block;
+
+/**
+ * The interface for "messages" (#type => status_messages) blocks.
+ *
+ * @see drupal_set_message()
+ * @see drupal_get_message()
+ * @see \Drupal\Core\Render\Element\StatusMessages
+ * @see \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
+ *
+ * @ingroup block_api
+ */
+interface MessagesBlockPluginInterface extends BlockPluginInterface { }