Distance along the alignment's basis curve from its start.
OptionalHasPset_Stationing.HasIncreasingStation; omitted when null or absent.
Pset_Stationing.IncomingStation — the station arriving here.
OptionalRoleGlobalId seed role; defaults to station-equation:<n> (1-based).
Pset_Stationing.Station — the station from here on.
One station equation (§14.1): all lengths in the file's length unit.