Group of Fields are meant to store other fields in order to sort data, present less information to the user, and even mask optional data. A group of fields appears as a Label with and Expand button. When clicked, all the other fields attached to the group are displayed. They can be hidden again by closing the group.

The name of the group is very important, as it is used by the other fields to specify the attachment. In the example below, there is a standard text field name, another text field surname, that is attached to group optional, and that group.

"fields": [
    { "name": "name", "label":"Name", "default": "Default value" },
    { "name": "surname", "label":"Surname", "group":"optional" },
    { "name": "optional", "label":"Optional fields", "type": "group", "expanded": false }
]

A group field don't use the default property. It has a property expanded, that indicates if the group is expanded (open) or not when accessing the card. By default, a group is not expanded.

There's no such thing as a variable for a group of fields.