This format can...
read and write waypoints
read and write tracks
read and write routes
Garmin documents only PCX5, an older format limited to the lame NMEA six-character waypoint names that's treated as a second-class citizen in current versions of MapSource. In Mapsource, use file->import to read these files. If you name the files *.wpt, Mapsource will find them more easily.
In general, you should prefer the "mapsource" file format to this one.
This format has been extended to handle many - but not all - files from GPS Utility. If you encounter something that GPSBabel does not handle well, use the free version of GPSUtil to read it and save as something more common.
Default icon name.
The deficon option is used to control the icon output when writing to this format. It overrides any icon information that might be present in the source data.