same <token> in the message.
+
The valid values for this option are: `addIfDifferentNeighbor` (this
-is the default), `addIfDifferent`, `add`, `overwrite` or `doNothing`.
+is the default), `addIfDifferent`, `add`, `replace` or `doNothing`.
+
With `addIfDifferentNeighbor`, a new trailer will be added only if no
trailer with the same (<token>, <value>) pair is above or below the line