Snap Dragon Doubles

After a competitive auction where the LHO opponent opens, partner overcalls and RHO responds a new suit, a double would show the 4th suit (at least 5) and support for partner (usually 3) Of course, the snap dragon doubler is not expected to have many hcp. 

opp part opp you
1H   1S   2C   x ; Showing diamonds and spade support
1S   2C   2D   x ; Showing hearts and club support 
1S   2C   2D  2H ; DENIES club support (else snap dragon)
1S   2C   2D  3C ; tends to deny having hearts