If the input elements to the differencing engine implement the IStructureComparator interface the engine recursively applies itself to the children of the input element. Leaf elements must implement the org.eclipse.compare.IStreamContentAccessor interface so that the differencer can perform a bytewise comparison on their contents.
One good example for this is org.eclipse.compare.ResourceNode which implements both interfaces (and more) for Eclipse workspace resources (org.eclipse.core.resources.IResource).
Another example is the DocumentRangeNode which can be used to compare hierarchical structures
that are superimposed on a document, that is where nodes and leafs correspond to ranges in a document
(org.eclipse.compare.contentmergeviewer.IDocumentRange).
Typically DocumentRangeNodes are created while parsing a document and they represent
the semantic entities of the document (e.g. a Java class, method or field).
The two subclasses JavaNode (in org.eclipse.jdt.internal.ui.compare)
and PropertyNode (in org.eclipse.jdt.internal.ui.compare) are good examples for this.
By default the differencing engine returns the result of the compare operation as a tree of DiffNode objects. However, this can be changed by overriding a single method of the engine.
Every DiffNode describes the changes among the two or three inputs.
A tree of DiffNodes can be displayed in a DiffTreeViewer. The DiffTreeViewer requires that inner nodes of the tree implement the IDiffContainer interface and leafs the IDiffElement interface.
The typical steps to compare hierarchically structured data and to display the differences would be to: