Indicates whether executions of the service requires serialization in documents or not. 
   Namespace:   Autodesk.Revit.DB.ExternalService  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2013 
Syntax
Remarks
 When a serializable service is executed in a document, a record about the executed server (or servers) is stored in the document's history. This allows active servers to be synchronized next time a saved document is opened in Revit. 
 Executions of a serializable service in a document must happen inside a transaction.