names=renew
visibility=public
kind=defined

--- renew(sec_or_renewer)
@todo

Reset the expiry time according to +sec_or_renewer+.

+nil+:   it is set to expire in the far future.

+false+: it has expired.

Numeric: it will expire in that many seconds.

Otherwise the argument refers to some kind of renewer object which
will reset its expiry time.

