Support Double

Used by opener to show exactly 3 trump support for responder's suit, whereas a direct raise shows 4 trump support.

             S: xxxx
             H: Axxx
             D: Qxx
             C: Qx

             S: x
             H: KQx
             D: KJxx
             C: Axxxx

W        N       E        S

                               1C
P        1H      1S       X
P        2H      P/O

Notes: South's double is a support (raise) double, showing exactly
3 trumps. If South bid 2H, he would show 4 trumps.