diff --git a/gtfs/spec/en/reference.md b/gtfs/spec/en/reference.md
index 39c4eabe..8debb598 100644
--- a/gtfs/spec/en/reference.md
+++ b/gtfs/spec/en/reference.md
@@ -514,22 +514,22 @@ For a given ordered pair of arriving trip and departing trip, the transfer with
| Field Name | Type | Presence | Description |
| ------ | ------ | ------ | ------ |
-| `from_stop_id` | Foreign ID referencing `stops.stop_id` | **Conditionally Required** | Identifies a stop or station where a connection between routes begins. If this field refers to a station, the transfer rule applies to all its child stops. Refering to a station is forbiden for `transfer_types` 4 and 5. |
-| `to_stop_id` | Foreign ID referencing `stops.stop_id` | **Conditionally Required** | Identifies a stop or station where a connection between routes ends. If this field refers to a station, the transfer rule applies to all child stops. Refering to a station is forbiden for `transfer_types` 4 and 5. |
+| `from_stop_id` | Foreign ID referencing `stops.stop_id` | **Required** | Identifies a stop or station where a connection between routes begins. If this field refers to a station, the transfer rule applies to all its child stops. Refering to a station is forbiden if `transfer_type` is `4`. |
+| `to_stop_id` | Foreign ID referencing `stops.stop_id` | **Required** | Identifies a stop or station where a connection between routes ends. If this field refers to a station, the transfer rule applies to all child stops. Refering to a station is forbiden if `transfer_type` is `4`. |
| `from_route_id` | Foreign ID referencing `routes.route_id` | Optional | Identifies a route where a connection begins.
If `from_route_id` is defined, the transfer will apply to the arriving trip on the route for the given `from_stop_id`.
If both `from_trip_id` and `from_route_id` are defined, the `trip_id` must belong to the `route_id`, and `from_trip_id` will take precedence. |
| `to_route_id` | Foreign ID referencing `routes.route_id` | Optional | Identifies a route where a connection ends.
If `to_route_id` is defined, the transfer will apply to the departing trip on the route for the given `to_stop_id`.
If both `to_trip_id` and `to_route_id` are defined, the `trip_id` must belong to the `route_id`, and `to_trip_id` will take precedence. |
-| `from_trip_id` | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes begins.
If `from_trip_id` is defined, the transfer will apply to the arriving trip for the given `from_stop_id`.
If both `from_trip_id` and `from_route_id` are defined, the `trip_id` must belong to the `route_id`, and `from_trip_id` will take precedence. REQUIRED if `transfer_type` is `4` or `5`. |
-| `to_trip_id` | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes ends.
If `to_trip_id` is defined, the transfer will apply to the departing trip for the given `to_stop_id`.
If both `to_trip_id` and `to_route_id` are defined, the `trip_id` must belong to the `route_id`, and `to_trip_id` will take precedence. REQUIRED if `transfer_type` is `4` or `5`. |
-| `transfer_type` | Enum | **Required** | Indicates the type of connection for the specified (`from_stop_id`, `to_stop_id`) pair. Valid options are:
`0` or empty - Recommended transfer point between routes.
`1` - Timed transfer point between two routes. The departing vehicle is expected to wait for the arriving one and leave sufficient time for a rider to transfer between routes.
`2` - Transfer requires a minimum amount of time between arrival and departure to ensure a connection. The time required to transfer is specified by `min_transfer_time`.
`3` - Transfers are not possible between routes at the location.
`4` - Passengers can transfer from one trip to another by staying onboard the same vehicle (an "in-seat transfer"). More details about this type of transfer [below](#linked-trips).
`5` - In-seat transfers are not allowed between sequential trips. The passenger must alight from the vehicle and re-board. More details about this type of transfer [below](#linked-trips). |
+| `from_trip_id` | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes begins.
If `from_trip_id` is defined, the transfer will apply to the arriving trip for the given `from_stop_id`.
If both `from_trip_id` and `from_route_id` are defined, the `trip_id` must belong to the `route_id`, and `from_trip_id` will take precedence. REQUIRED if `transfer_type` is `4`. |
+| `to_trip_id` | Foreign ID referencing `trips.trip_id` | **Conditionally Required** | Identifies a trip where a connection between routes ends.
If `to_trip_id` is defined, the transfer will apply to the departing trip for the given `to_stop_id`.
If both `to_trip_id` and `to_route_id` are defined, the `trip_id` must belong to the `route_id`, and `to_trip_id` will take precedence. REQUIRED if `transfer_type` is `4`. |
+| `transfer_type` | Enum | **Required** | Indicates the type of connection for the specified (`from_stop_id`, `to_stop_id`) pair. Valid options are:
`0` or empty - Recommended transfer point between routes.
`1` - Timed transfer point between two routes. The departing vehicle is expected to wait for the arriving one and leave sufficient time for a rider to transfer between routes.
`2` - Transfer requires a minimum amount of time between arrival and departure to ensure a connection. The time required to transfer is specified by `min_transfer_time`.
`3` - Transfers are not possible between routes at the location.
`4` - Passengers can transfer from one trip to another by staying onboard the same vehicle (an "in-seat transfer"). More details about this type of transfer [below](#linked-trips). |
| `min_transfer_time` | Non-negative integer | Optional | Amount of time, in seconds, that must be available to permit a transfer between routes at the specified stops. The `min_transfer_time` should be sufficient to permit a typical rider to move between the two stops, including buffer time to allow for schedule variance on each route. |
#### Linked trips
-The following applies to `transfer_type=4` and `=5`, which are used to link trips together, with or without in-seats transfers.
+The following applies to `transfer_type=4`, which is used to link trips together with in-seats transfers.
The trips linked together MUST be operated by the same vehicle. The vehicle MAY be coupled to, or uncoupled from, other vehicles.
-If both a linked trips transfer and a block_id are provided and they produce conflicting results, then the linked trips transfer shall be used.
+If the trips associated with an agency include any linked trip in-seat transfers, as specified via `transfer_type=4`, then no implicit in-seat transfers should be created using `block_id`-based heuristics for any trips associated with that agency.
The last stop of `from_trip_id` SHOULD be geographically close to the first stop of `to_trip_id`, and the last arrival time of `from_trip_id` SHOULD be prior but close to the first departure time of `to_trip_id`. The last arrival time of `from_trip_id` MAY be later than the first departure time of `to_trip_id` in case the `to_trip_id` trip is occurring the subsequent service day.