A double by opener on the second round when both
sides have found a fit and there is no room for any other game try.
The double shows a hand strong enough to invite game.
South West North East
1S 2H 2S 3H
Dble
It follows that a bid of 3S by South would suggest simply a desire to
contest the partscore.
In this example, if the defending side's suit were diamonds or clubs,
a double would have its ordinary penalty meaning.