DiffPlug doesn’t force you to diff entire files. You can choose to diff only certain subsystems or states, or perhaps even two subsystems from the same file. Simply drag from one model element and drop onto any other to begin a subdiff. You can drag and drop from the graphical diagram or tree view of any view or diff.
The purpose of the greyed-out elements is to show you which elements you are comparing.
Once dropped, you’ll be presented with one or two options:
This option will only be available if both the dragged and dropped elements are container objects, such as Subsystems or Subcharts. If you select this option, DiffPlug will recursively compare all of the children of these objects.
This option will always be available. It compares only the detail properties of the dragged and dropped elements.