clarified in the config comment instructions that 'permitted_uri_chars' is a regular expression
diff --git a/system/application/config/config.php b/system/application/config/config.php
index 72d3819..6a7b857 100644
--- a/system/application/config/config.php
+++ b/system/application/config/config.php
@@ -111,9 +111,9 @@
| Allowed URL Characters
|--------------------------------------------------------------------------
|
-| This lets you specify which characters are permitted within your URLs.
-| When someone tries to submit a URL with disallowed characters they will
-| get a warning message.
+| This lets you specify with a regular expression which characters are permitted
+| within your URLs. When someone tries to submit a URL with disallowed
+| characters they will get a warning message.
|
| As a security measure you are STRONGLY encouraged to restrict URLs to
| as few characters as possible. By default only these are allowed: a-z 0-9~%.:_-