Macro help

[Rein]

I can't seem to find anywhere that will tell me how to dot several enemies useing a macro. Does anyone know a script as on how to DoT 3 enemies with Siphon Life.

Maybe somthing like tab (to select the closest enemy) then cast siphon life, tab, siphon life, tab, and siphon life for the last enemy. I just wanted it for when i'm pvping and there are multiple players that attack me at once as an unfair advantage (you all know it happens). this way i can fight back with all i can. I think 3 enemies is a good number as so i don't use up all my mana and i don't waste all my time casting siphon life and never doing any real damage.

I want to learn macros and i don't really know where to start, i guess here
if anyone can help me with this i would greately appreciate it.