[JASS] ForGroup and the Enum Functions

[Vosty]

You know, I've benn Jassing for over a six months now.
And there is one thing that is seems like I am never using, and when I do use it, it seems as if I am doing it wrong.
These things are the ForGroup, and more often the Enum functions.
I always see them in scripts, and I have a ok guess at what they do. Can someone clear up my last doubts by shedding a few examples?

 

[TriggerHappy]

function EnumFunc takes nothing returns nothing
   call BJDebugMsg(GetUnitName(GetEnumUnit())) // Dispalys the picked unit.
endfunction

function main takes nothing returns nothing
    local group g = CreateGroup() // It's better to re-use a global group
                                 // but for the sake of simplicity, I shall do this.
    call GroupEnumUnitsInRange(g, 0, 0, 500, null) // Picks all units withing 500 of Location(0,0)
    call ForGroup(g, function EnumFunc) // Do something with the group.
endfunction

 

[Vosty]

Okay, I get the Forgroup part.
What is the first parameter for the GroupEnumUnitsInRange for? Is is storing it to that variable? Is is picking units only in that group for the enumeration? I'm a bit confused there.
Btw, the null part is for a filter, right?

 

[TriggerHappy]

It adds all the units to the group 'g'.

 

[axleion]

native GroupEnumUnitsInRange                takes group whichGroup, real x, real y, real radius, boolexpr filter returns nothing

 

[Vosty]

ok, thanks!

 

[azlier]

Not only does it add the units to the group, but it clears the group beforehand. Just to add more info.