PosInfos is a magic type which can be used to generate position information
into the output for debugging use.
If a function has a final optional argument of this type, i.e.
(..., ?pos:haxe.PosInfos), each call to that function which does not assign
a value to that argument has its position added as call argument.
This can be used to track positions of calls in e.g. a unit testing framework.