A text field which contains the allowed filtering expressions for the allowed URLs. Use of the wildcard char '\*' is possible. Examples for expressions: 'example.com' or 'example.com/stuff/\*'. 'example.com' matches 'example.com', 'www.example.com' and 'www.mail.example.com'. 'example.com/stuff/\*' matches all requests to any subdomain of 'example.com' that have 'stuff' as the first segment of the path.