#chapter Relations Between (Graphical) Objects

The first part of this chapter discusses lines connecting two graphical
objects implemented by the classes connection, link, handle and
graphical.  The second part discusses general PCE maintained binary
relations between objects.

Besides the material described in this chapter, the following is
relevant for handling relations between objects:

	# class graphical
	The section on relations discusses methods for handling
	connection objects from the viewpoint of the connected
	objects.

	# class hyper
	A hyper is a general binary relation object which facilates
	communication (=passing messages) between the connected objects.

The first cluster (connection/link/handle) describe a line that is
automatically updated if either of the connected graphical objects'
geometry or <-device changes.  The connection object describes the
*instance*.  A link is a generic description for a group of connections,
defining both the appearance and the association with handles.  A handle
object is a named connection-point that may be attached to a graphical
or a graphical's class.

In the second cluster, a constraint is an instantiation of a relation
object.  A relation describes the properties its individual constraints.
#end chapter

#class connection
#end class

#class link
#end class

#class handle
#end class

#class constraint
#end class

#class relation
#end class

#class identity
#end class

#class spatial
#end class