Here's an illustration of a Wedge Christie.
Brushing, yes. Is it intentional, or simply inevitable? Positive ("ski tips into the turn") or negative ("tails intentionally pushed out to a skid") movements?
Look closely and you can see that, from the start of each turn, both skis turn in the direction of the turn, and they both turn in the same direction, simultaneously and continuously. Yes, the outside ski turns more quickly than the inside ski in the initiation of a wedge christie (causing the wedge), but it is NOT intentional. The skier is simply trying to turn both skis into the turn--parallel--but due to the complexities of rotating one leg internally while rotating the other externally, combined with the different amounts of resistance of each ski, it is difficult to keep them parallel. For skiers of this novice skill level, the result of this attempt to make an offensive, gliding, direction-control parallel turn is...a wedge christie!
(And even advanced skiers can demonstrate the same phenomenon. Start from a stop, with parallel skis, and make a very tight radius "basic parallel" turn with NO NEGATIVE MOVEMENTS, and see for yourself!)
Note too that in addition to the rotary movements (tips into the turn), tipping movements and pressure control movements and movements of the center of mass also tend in the direction of the turn. Tipping movements, like rotary movements, are also simultaneous--both skis "roll" to the right or to the left at the same time, although not necessarily at the same rate
. Turns begin with an edge release--a "letting go" of the mountain, not necessarily "flat" skis. Once you let go, there is no "platform" from which to push the uphill tail out into a skid ("stem"). In a right turn, nothing moves (intentionally, at least) left.
This is the "American" Wedge Christie, as defined by PSIA's Center Line™ Model of the late 1980's, as I envision it. There are certainly many other ways to make "turns" that start with a wedge and finish parallel--and each can be "correct," depending on the skier's intent. But this is the one identified as a clear "milestone" in the development of skill from beginner to advanced. The critical concept is that, fundamentally, the movements and skier intent (to "go that way," rather than to brake or "stop going this way") are the exact same from first turns on. It's what the Center Line™ Model would have called "linear learning"--increasing skill and getting better at doing the same thing. It fits with the ideal that "we don't teach beginner skiing--we introduce beginners to the skiing of experts!"
It's also critical to recognize that the Center Line™ Model recognized "lateral learning" as well--developing fundamentally different movement patterns to serve different intents and purposes. So TDK6's Stem Christie (with intentional "negative" tails-out movements to create a skid, as he describes) is also an important movement pattern and skill blend, and something we should be able to "teach" when necessary. But it is simply not part of a LINEAR progression from first turns to advanced parallel (offensive) turns.
That is all!