>>>It looks like the guy in that image isn't using his ski's edges at all. It appears that all he's doing is making quick skidded turns.<<<
Exactly. That's what wedeln is. It is used on mostly flat terrain where a heavier edge set would slow forward speed too much. As the terrain gets steeper we set the edge as hard as needed and we call this short swing. The body still faces downhill and doesn't appreciably deflect from a straigh shot down the fall line.
When it gets steeper yet, the hard edge set affords a rebound and is used as Si mentioned, using rebound enough to lighten but not bounce you up and then retracting the skis, moving them underneath the body to the other side. In space deprived corridors this is really useful.
On the other hand, staying with the edge set a fraction longer wil carve the ski farther to the outside and the body mass will now leave the straight downhill path weaving from side to side, and as the the carves get longer in medium to long turns, cross-under or cross-over can be used.
If a check with rebound is used at the end of the turn and the skis are retracted and moved to the other side quickly I would call it a cross-under since the path of the body is not influenced, but if at the edge set at the end of the turn the lower leg is relaxed allowing the body to flow across the anchored skis I would call it a cross-over.
But who cares what it is called, you use whatevr you need or want [img]smile.gif[/img]
BTW, pa_twoplanker, wedeln on almost flat skis is harder to do than you imagine, try it sometime