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. 

Examples:
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