docs: update Custom validation rules

Author: kenjis

docs/customization.md

@@ -95,8 +95,14 @@ Shield has the following rules for registration:
 
 ```php
 [
-    'username'         => 'required|alpha_numeric_space|min_length[3]|is_unique[users.username]',
-    'email'            => 'required|valid_email|is_unique[auth_identities.secret]',
+    'username'         => [
+            'required',
+            'max_length[30]',
+            'min_length[3]',
+            'regex_match[/\A[a-zA-Z0-9\.]+\z/]',
+            'is_unique[users.username]',
+        ],
+    'email'            => 'required|max_length[254]|valid_email|is_unique[auth_identities.secret]',
     'password'         => 'required|strong_password',
     'password_confirm' => 'required|matches[password]',
 ];
@@ -109,8 +115,14 @@ If you need a different set of rules for registration, you can specify them in y
 // Rules
 //--------------------------------------------------------------------
 public $registration = [
-    'username'         => 'required|alpha_numeric_space|min_length[3]|is_unique[users.username]',
-    'email'            => 'required|valid_email|is_unique[auth_identities.secret]',
+    'username'         => [
+            'required',
+            'max_length[30]',
+            'min_length[3]',
+            'regex_match[/\A[a-zA-Z0-9\.]+\z/]',
+            'is_unique[users.username]',
+        ],
+    'email'            => 'required|max_length[254]|valid_email|is_unique[auth_identities.secret]',
     'password'         => 'required|strong_password',
     'password_confirm' => 'required|matches[password]',
 ];