[Zope] why two session identifiers?

Dear list, could anybody tell me why the Session product assigns a session id AND a session token to a session? I've noticed that expiration of the session data object causes (on a further request) the session id to change, while the token stays the same: any explications? Thanks, Mario. _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx