Line 368 - Both DtStart and Duration are "optional". What precisely does that mean? That neither need to be present? we find later that these values can be inherited from a gluon, but at this point "optional" seems to mean "no value is required"

Added language explicitly calling out Binding: Identifies length of time for Interval. Duration must be known before an Interval can be transacted, but the Duration may only come through Binding. Scheduled start date and time for Interval. The Start must be known before an Interval can be transacted, but the Duration may only come through Binding