An NSString object containing an integer value stating how long in seconds the cookie should be kept, at most.
Only valid for Version 1 cookies and later. Default is “0”. This field is optional.
Available in Mac OS X v10.2 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)