Group class is responsible for the complete layout of a MUI window. A group may contain any number of child objects, maybe buttons, cycle gadgets or even other groups.
Some attributes of group class define how the children of a group are layouted. You can e.g. tell your group to place its children horizontally (in a row) or vertically (in a column). Since every MUI object knows about its minimum and maximum dimensions, group class has everything it needs to do that job.
More sophisticated layout is possible by assigning different weights to objects in a group or by making a group two-dimensional.
Beneath the layout issues, a group object passes attributes and methods through to all of its children. Thus, you can talk and listen to any child of a group by talking and listening to the group itself.