Difference between Container and ContainerStruct

Hi,

I'm studying the Stellaris GRLIB . 

Reading the demo all RadioButtonStruct of the "g_psRadioButtons1[]" array  are grouped with a reference to their father : g_psRadioContainers which is a ContainerStruct.

Why dont use as father directly a Container instead? Reading the manual both are global macro to build at compile time the tree.

Which is the difference between ContainerStruct and Container ? 

If I have  just to draw 3 grouped radiobutton   why dont use a simple container widget instead of I containerStruct as father l?

Hope in help thanks in advance