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sure thing, sam. santi is probably the coolest thing in xingyiquan. it looks deceptively-simple, but it is actually very powerful. when you decide to take up xingyiquan, you will be very pleased with it. it is not nearly as brazen and simple as many people superficially think it to be.
the differences that you are liable to see are usually small. things that are most noticable are the distance of the feet from eachother, the angle the hips are twisted at, whether the rear hand is closed or open, and weight distribution. these are quite small differences, besides the hip direction, so you don’t need to worry about the differences very much.
for the rear foot positioning, you should imagine a straight line going from your baihui down to your yongquan cavities in your feet. this distributes the majority of the weight on your back leg. the front foot is placed as far as it will go in front of your back leg (this will not very very far at all) without changing your weight distribution. make sure that your front leg is bent, and not sunken down, as well. there are no real weight distribution numbers. when you keep the vertical line of weight distribution everything else goes into place. this weight distribution on one leg is referred to in the classics as the “chicken’s legs”.
the hips twist so you face directly forward. this twisting of the body is what the classics refer to as the “dragon’s body”.
the hands are held upward so there is a bit of strain in the wrists, and the fingers should be spaced out a bit. this is called the “eagle’s claws”.
the back should be stretched, and the chest relaxed by rounding the shoulders forward. this is called “bear’s shoulders”.
these are a few of the rudimentary characteristics of santi.
as for stepping, there are a few stances that are used very regularly, and then a few that are not used very often. the stance that you see in santi is the main one. the next is done by rotating the leading foot outward 45 degrees. the next is practiced by placing the rear foot next to the leading foot (albeit slightly behind it). other stances are not used nearly as often. all stances are generally quite high, though, except for the scissors stance and the lowered stance in the snake form.
there is only so much i can type, though, so i’d head over to:
http://www.emptyflower.com/xingyiquan
to get my fix of xingyiquan. best site around, in my opinion. it’s a treasure chest of information on xingyiquan, as well as practitioners much better than myself. 