The client's own metadata about the track, stored as posted and returned in the track's properties, so the API does not have to grow a field for every such use.
OptionalcontextThe vessel this track belongs to, when the client knows.
Supplying it associates the import with a vessel in the data model; it does not merge the import into that vessel's recorded track, which stays separate and separately addressable.
OptionalcoordRecording time of every point, nested to match coordinates.
Optional because not every GPX carries <time>. A track without times is
still a track, a shape someone sailed, but it cannot answer a time window
query, and a provider may refuse it for that reason. A provider that
accepts one returns it with no from or to, which are optional for
exactly this case.
OptionalnameThe track's own name, typically a GPX <trk><name>.
What a client said about a track it offers for storage.