adding garmin extensions

[Sprechen]

I need to add information to my trk infos, specifically I need to add the speed of each point in the segment.
This is defined by the garmin extension https://www8.garmin.com/xmlschemas/TrackPointExtensionv2.xsd.
As I understand, for each point I can use the extensions map to add additional data for each Wpt point, but how I can add schemas to the Gpx node?

[kb0]

It's possible to use GpxWriter().asXml. For ex.:

final gpxXml = GpxWriter().asXml(gpx);
gpxXml.children[1].setAttribute("xmlns:trp", "http://www.garmin.com/xmlschemas/TripExtensions/v1");
gpxXml.children[1].setAttribute("xsi:schemaLocation", "http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd");
gpxXml.toXmlString()

[Sprechen]

It's possible to use GpxWriter().asXml. For ex.:

final gpxXml = GpxWriter().asXml(gpx);
gpxXml.children[1].setAttribute("xmlns:trp", "http://www.garmin.com/xmlschemas/TripExtensions/v1");
gpxXml.children[1].setAttribute("xsi:schemaLocation", "http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd");
gpxXml.toXmlString()

Ok thank you! So, no native support for that!
Maybe, I can make a pull request with this feature