How to specify current density in FEM solver?

I have a few questions about a specific part of the Matlab FEM solver because the documentation isn't clear from what I can see:

1) For this specific problem statement I cannot figure out what are the units of the current density specifed in the line:

electromagneticSource(model3D,"CurrentDensity",@windingCurrent3D,"Cell",3)

Is this Amps/m^2, Amps/m^3, etc.? I'm not sure why this isn't specified in the documentation. I am assuming it should be m^-2 but I am not sure.

2) The function it calls "@windingCurrent3D" has two input arguments called "region" and "~". I don't understand why there are two input arguments for this function and again, it doesn't specify how and why it is able to accept an input when the example isn't showing an input argument being defined when the function is called here. Moreover, it is saying that it is taking some input called "region", and breaks it down into cartesean components but where are these coming from?

function f3D = windingCurrent3D(region,~)

[TH,~,~] = cart2pol(region.x,region.y,region.z);

f3D = -5E6*[sin(TH); -cos(TH); zeros(size(TH))];

end

3) If I want to specify a given, total current I for the solenoid, how can I pass this into the windingCurrent3D function? Or can I just define my own within my version of the code that doesn't need to call a seperate function file? This is something else that the documenation doesn't elaborate on: What are all the objects that I can pass as input arguments for "CurrentDensity"?

I wish this documentation went into more detail as to what's going on here. Even when reading other example use cases and problems with this toolbox, I am not seeing any explanations for current density explictly and so I am very confused.