The GUID portion of the DocumentVersion. The GUID is updated when changes are made to the document, but may not update with every change to the document. The GUID and save number are both necessary to uniquely identify a document version.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0)
Since: 2015