SWI-Prolog -- Instance variables

connection <- fixed_from: bool: The slots connection<-fixed_from and connection<-fixed_to are used internally to represent that the handles the connection is related to (connection<-from_handle and connection<-to_handle) should not be reconsidered if the connection is updated. These values are normally @off and set to @on by connection->initialise if the corresponding handle is specified.
connection <- fixed_to: bool: Inherits description from: connection-fixed_from
connection <- from: graphical*: Related graphical and the indicated end of the connection. See also graphical<-connections, graphical<-connected,‘connection connection<-opposite’.
connection <- from_handle: name*: Name of the handle used at the indicated end. Depending on connection<-fixed_from/fixed_to, this handle is or is not updated if either of the connected graphicals is moved or changed otherwise.
connection <- to: graphical*: Inherits description from: connection-from
connection <- to_handle: name*: Inherits description from: connection-from_handle