The descriptions of the FormularyItem included extensions are derived from the extension StructureDefinition descriptions. These StructureDefinitions will be updated with the following descriptions. usdf-FormularyReference-extension    Description: Reference to the formulary this item belongs to. usdf-AvailabilityStatus-extension Description: A boolean indicating whether the formulary item is currently available under the formulary. Drugs may appear on a formulary, but not considered "active" for the current year. Drugs may also be removed during the course of a plan year. usdf-AvailabilityPeriod-extension Description: The period for which this item is available on the formulary. Drugs may appear on a formulary, but not considered "active" for the current year.  usdf-StepTherapyLimit-extension Description: A boolean indicating whether the coverage plan imposes a step therapy requirement on this drug meaning another drug may need to be tried beforehand. usdf-StepTherapyLimitNewStartsOnly-extension Description: A boolean indicating whether the coverage plan imposes a step therapy requirement on this drug meaning another drug may need to be tried beforehand for new starts only (Not required if patient has previously met step therapy requirements).  (Only include if StepTherapyLimit = true) usdf-QuantityLimitDetail-extension Description: A detailed definition of the quantity limits the coverage plan imposes on this drug. These limit details may include (potentially including a rolling dispense limit, maximum daily, or therapy days for a period of time. (Only include if QuantityLimit = true)