The Shimano XT M780 and M785 are designed to work with Shimano's 10 speed mountain groups. The M780 is for use with 2x10 while the M785 is for a 3x10 set up. The difference being in the cage profile. A 2x10 crank requires a smaller diameter cage with a different throw and conversely, a triple crank requires just the opposite.
The Top Swing designation means that the cage swings above or on top of the clamp, hence top swing. The clamp is black anodized and matches the rest of the 780 series components while the cage is coated for added durability and chain glide. Set screws are located on the outside of the derailleur for easy adjustment. When it comes to front derailleurs, no one does it better than Shimano.