[ci skip] Formally deprecate 'global_xss_filtering'
diff --git a/application/config/config.php b/application/config/config.php
index 7d5c24c..7be482b 100644
--- a/application/config/config.php
+++ b/application/config/config.php
@@ -404,6 +404,9 @@
 | Determines whether the XSS filter is always active when GET, POST or
 | COOKIE data is encountered
 |
+| WARNING: This feature is DEPRECATED and currently available only
+|          for backwards compatibility purposes!
+|
 */
 $config['global_xss_filtering'] = FALSE;