Top and grouping object that helps to form structures
 in the Plant Hierarchy in the Plant Configuration.

 A ProviewR system can have several $PlantHier objects
 placed on the top level or below another $PlantHier
 object.
 The object is used in the Plant Configuration in a way
 analog to the $NodeHier object in the Node
 Configuration.

 Is created in the development environment by means of
 the Configuration Editor.

 Contains no relevant information (=data) in rtdb.

 Optional text to describe the use of the object.

 A XttGraph object that will open a graph that contains data for
 this hierarchy. This graph can be opened from the popup menu for
 this object.

 A DsTrend or PlotGroup object that contains trend for this hierarchy.
 The trend can be opened from the popup menu for this object.

 A help topic in the xtt help file that contains help for this hierarchy.
 The help can be displayed from the popup menu for this object.

 A URL to the data sheet for the equipment in this hierarchy.
 The data sheet can be displayed from the popup menu for this object.

 An URL to the circuit diagram for the equipment in this hierarchy.
 The circuit diagram can be displayed from the popup menu for this object.

 If the attribute is empty, the CircuitDiagram method will look at the
 closest ancestor that has supplied a value in CircuitDiagram and use this
 URL instead. If this behavior is unwanted, put the string 'Disabled' in the
 attribute. This will disable the CircuitDiagram method for this object, and
 for any child with empty CircuitDiagram attribute.

 A photograph of the plant.
 A URL to a photo of the equipment.
 The photo can be displayed from the popup menu for this object.

 Configuration status.
 Status in the development environment for an hierarchy,
 plcprogram or process graph, set by the designer to indicate
 the current state. If a status is set for an object, it is
 marked red, yellow or green in the configurator. Also the
 status text if viewed surrounded by angel brackets.

 Safety level.
 Safety level in the development environment for an hierarchy,
 plcprogram or process graph, set by the designer to indicate
 the level. If a level is set for an object, it is marked with
 a warning trangle.