In game help located in +help dtu rider.
Betweening commands:
dtu learn <alias>=<dbref> Learn <dbref> as <alias>.
dtu learn <alias>=here Learn your dragon's location as <alias>.
dtu learn <alias>=<dragon> Learn <dragon>'s image as <alias>.
dtu image <alias> Image <alias> (for the last 'dtu learn')
dtu image Clear image.
dtu forget <alias> Remove an alias.
dtu btw <alias> Between to <alias>
dtu btw Between to your image.
dtu dests List of destinations.
dtu jump <dbref> Jump directly to room <dbref> (more below).
'dtu btw' and 'dtu image' and 'dtu learn' will 'safely' refuse, if the location is unbetweenable (ie not a room, or not enter_ok). However, 'dtu jump' is a more IC version of betweening to a location you do not know, and should be used carefully. If the room in question is not beweenable, the dragon (and, presumably, the rider, and anyone else on the dragon) is Lost Between. (This /can/ be retconned, but… :)
