I have added support for Int64 constructor arguments. For now, I would recommend using a double.
Specifying the type of the argument in the attribute is redundant, since we can just get that information via reflection. So as of the next release, we won't even be looking at what the attribute says the type is. The only thing we will use the attribute for is to get the name and default value of the argument.
The supported argument types are string, Int32, Int64, double, BarElement, and Boolean. The ChartPane and UserDefined ConstructorArgumentTypes are not really supported.
You can also define your own enumeration, and use it for a constructor argument. This is quite useful when you have multiple options. The comparison trigger currently uses this functionality to let you choose the comparison type. Note that enum constructor arguments were not really supported in the current release (build 322), but they will be in the next release.