Gets or sets a key associated with the user data for this UserTrackingRecord.
Assembly: System.Workflow.Runtime (in System.Workflow.Runtime.dll)
An activity or workflow designer can use either ActivityExecutionContext.TrackData(String, Object) or Activity.TrackData(String, Object) to specify a key to associate with the user data pushed to the runtime tracking infrastructure. contains this key. If no key is specified, is a null reference (Nothing in Visual Basic).