I never understood that. You could have macros to do that much more easily!
Code:
/cast [target=focus,help,exists,nodead,modifier:ctrl] Regrowth; [target=mouseover,help,exists,nodead] Regrowth; [target=target,help,exists,nodead] Regrowth; [target=player] Regrowth;
1) if exists focus and pressed CTRL cast Regrowth on focus
2) if exists mouseover cast Regrowth on mouseover
3) if exists target cast Regrowth on target
4) else cast Regrowth on player
This is so much functionality in just one simple macro.