Please keep in mind, the Group type is not for grouping items, but for adding an element which members are the members of a group (defined in your items file).
For grouping items you should consider Frames as you already do, and but they can not be nested. Or use Text, that will create a sub level.
I know But I used it since openHAB 1.X for nesting loose items
I was curious about this because I tried to port my openHAB2.0 config to openHAB 2.2 and got erros and warns.
@gersilex is this worth opening an enhancement issue on github?
I really liked the feature / bug that you can use Groups to create manual nesting.
or @Kai is there an equivalent for nesting items manual ?
Another text element showing a “Multimedia” summary, e.g. “Currently playing”. The element is additionally the host for a nested block. By clicking in the element, a new view with two elements is presented