Specifies how cookies are used for a Web application.

The cookieless attribute can be one of the following possible values.
The default is the UseCookies value.

Note When you configure an AJAX-enabled ASP.NET Web site,use only the
default value of UseCookies for the cookieless attribute. Settings
that use cookies encoded in the URL are not supported by the ASP.NET
AJAX client script libraries.

Value Description

AutoDetect ASP.NET determines whether the requesting browser or device supports cookies. If the requesting browser or device supports
cookies,AutoDetect uses cookies to persist user data; otherwise,an
identifier is used in the query string. If the browser or device
supports cookies,but cookies are currently disabled,cookies are
still used by the requesting feature.

UseCookies Cookies persist user data,regardless of whether the browser or device supports cookies.

UseDeviceProfile ASP.NET determines whether to use cookies based on the HttpBrowserCapabilities setting. If the HttpBrowserCapabilities
setting indicates that the browser or device supports cookies,cookies
are used; otherwise,an identifier is used in the query string.

UseUri The calling feature uses the query string to store an identifier,regardless of whether the browser or device supports
cookies.

还看看http://msdn.microsoft.com/en-us/library/h6bb9cz9.aspx