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vtkMRMLLayoutNode: Node that describes the layout of the views. There is only one layout node in the scene (singleton)
vtkMRMLLayoutLogic: Control/observe the layout node. Automatically create the view nodes if needed (referenced in the layout node description but not in the scene).
vtkMRMLAbstractViewNode: Abstract class for all the view nodes (such as vtkMRMLSliceNode, vtkMRMLViewNode, vtkMRMLChartViewNode) that can be into a layout.
ctkLayoutManager: Mechanism to convert the layout description (xml) into a Qt layout with Qt widgets.
qMRMLLayoutManager: Specialized version of ctkLayoutManager to handle MRML only views and properties.
qSlicerLayoutManager: Specialized version of qMRMLLayoutManager to handle Slicer specific behaviors. The Slicer layout manager is accessible from the qSlicerApplication singleton.