Nodes in the visual tree can be either Visual or Visual3D objects. Methods that are specific to a type of visual object are typed as either Visual or Visual3D. However, some methods in the VisualTreeHelper class can accept a DependencyObject value that represents either type of visual object.
WPF supports programmatic access to several different tree structures of objects. Primarily, this is exposed as a visual tree and a logical tree. In some cases, the logical tree is a more useful representation of the elements in a WPF application, but conceptually the logical tree is implemented at a level beyond the Visual class. Unlike the visual tree, the logical tree can represent nonvisual data objects, such as ListItem. For more information on the logical tree, see Trees in WPF. The logical tree also is supported by a similar utility method class, LogicalTreeHelper.
The following example shows how to enumerate all the descendants of a visual object, which is a technique you might want to use if you were interested in serializing all the rendering information of a visual object hierarchy.