The key "Group1" should return a list of the objects, characters or locations that are in that group.
Group1 should return Object4|Object6|Object397 so that it can be used as a parameter when an action executes a task with an %object% reference, causing the task to be run for each object in the group.
Group1.List should print the group members, eg:
The torch, the lantern and the glow worm.
Group1.Count should return the current number of items in the group.
One minor niggle is that "Group1" by itself is not a valid OO function when embedded directly into text, but, as there is no reason to use it outside of an execute task parameter, it should not be a problem.
If you did want to print the group then you could just use the embedded expression <#Group1#>