Link groups to other objects.
Hierarchy
Groups can be linked to objects that are above or below,
in the Gamgi hierarchy. Pressing the button 
Below (the default), 
the 
Objects menu shows the classes of objects that can be owned 
by groups: Group, Plane, Direction, Atom (the default), Orbital and Text. 
Pressing the button 
Above, the same menu shows the classes of objects 
that can own groups: Layer (the default), Assembly, Cell, Cluster, Molecule
and Group. Groups can own other groups (they are recursive objects), so they 
can be linked above or below to other groups. 
Object
Gamgi expects users to identify first the group or list of groups
and then the object to link. When the 
Group entry is active
and empty, clicking the mouse over a group, on the current layer
(local selection), its identification is transported to the 
Group
entry. Gamgi is now expecting users to click on a object of the 
class currently selected in the 
Object menu. This object 
can be in a different layer or even in a different window (global 
selection). 
To select a visible object in a different layer, in the same window, 
just press the mouse over the object, as if it was in the current 
layer. To select objects without visual representation, as layers
and lights, press the mouse over the graphic area in the window,
to create a menu with all the objects of that class in the window, 
which can then be selected. To select an object in a different window, 
with the mouse, use exactly the same procedure, in that window.
Link
Gamgi suppports only one type of linking mode for Group: 
Object.
The 
Object method links a group to a single 
Object. 
When the 
Hierarchy is 
Above, the group is unlinked 
from its current parent and linked to the object. When the group 
is moved to a different layer, all its bonds to other objects are 
automatically removed. When the 
Hierarchy is 
Below, 
the object is unlinked from its current parent and linked to 
the group. 
When the new child previously owned the new parent (a situation made 
possible because groups can own other groups), the new parent 
is first linked to the new child parent. An error is issued when the 
parent already owned the child object.
After the linking operation, Gamgi always puts on top
the window and layer containing the linked objects.