diff --git a/user_guide/libraries/security.html b/user_guide/libraries/security.html
index a50d948..6d6216d 100644
--- a/user_guide/libraries/security.html
+++ b/user_guide/libraries/security.html
@@ -102,6 +102,11 @@
 
 <code>$filename = $this->security->sanitize_filename($this->input->post('filename'));</code>
 
+<p>If it is acceptable for the user input to include relative paths, e.g. <kbd>file/in/some/approved/folder.txt</kbd>, you can set the second optional parameter,
+	<samp>$relative_path</samp> to TRUE.</p>
+	
+<code>$filename = $this->security->sanitize_filename($this->input->post('filename'), TRUE);</code>
+
 <!-- @todo write docs for CSRF methods -->
 
 </div>