<para>
  Write Garmin-specific extensions, when such data is available, to the GPX.
  Notably, depth, temperature, proximity, display color, ambient temperature,
  heart rate, and cadence are read when they are available in the source data.
  This data can, of course, only be read by GPX readers that know about the
  Garmin gpxtpx and gpxx extended namespaces.
</para>
<para>
Implies <option>gpxver=1.1</option>
</para>
