docs: Note about switching types in session

Author: neznaika0

user_guide_src/source/libraries/sessions.rst

@@ -344,6 +344,15 @@ intend to reuse that same key in the same request, you'd want to use
 
 .. literalinclude:: sessions/036.php
 
+Flag Manipulation
+=================
+
+Since the data is stored in the session and the Flashdata/Tempdata methods only manipulates flags, you can change the type for one value.
+
+.. literalinclude:: sessions/045.php
+
+You may never use it, but know that it works.
+
 Closing a Session
 =================
 

user_guide_src/source/libraries/sessions/045.php

@@ -0,0 +1,25 @@
+<?php
+
+session()->setFlashdata('alerts', 'Operation success!');
+
+/**
+ * Get flash value 'Operation success!' in another controller.
+ *
+ * echo session()->getFlashdata('alerts');
+ */
+
+// Switch flag
+session()->markAsTempdata('alerts');
+
+// or rewrite
+session()->setTempdata('alerts', 'Operation success!');
+
+/**
+ * Get temp value 'Operation success!' in another controller.
+ *
+ * echo session()->getTempdata('alerts');
+ *
+ * But flash value will be empty 'null'.
+ *
+ * echo session()->getFlashdata('alerts');
+ */