anchor.diff:                      | None         -> return! this.WriteStreamToBodyAsync stream None
                       | Some ranges  ->
                           // Check and validate If-Range HTTP header
  -                        match RangeHelper.matchesIfRange this.Request eTag lastModified with
  +                        match RangeHelper.isIfRangeValid this.Request eTag lastModified with
                           | false -> return! this.WriteStreamToBodyAsync stream None
                           | true  ->
                               match RangeHelper.validateRanges ranges stream.Length with
  
positive.code:                     Ok { Start = startOfRange; End = endOfRange }
  
      /// Helper method to parse and validate the If-Range HTTP header
      let matchesIfRange (request      : HttpRequest)
                         (eTag         : EntityTagHeaderValue option)
                         (lastModified : DateTimeOffset option) =
          let ifRange = request.GetTypedHeaders().IfRange
  
negative.code:                                  (lastModified          : DateTimeOffset option) =
          task {
              match this.ValidatePreConditions eTag lastModified with
              | ConditionFailed -> return this.NotModifiedResponse()
              | NotModified     -> return this.PreConditionFailedResponse()
  
              // If all pre-conditions have been met (or didn't exist) then proceed with web request execution
              | IsMatch | NotSpecified ->
  