I am in the process of removing a crappy shower stall and I am
planning to tile the shower area.

I plan to use concrete backer board in the area that will be tiled.

My question is how do I transition from the backer board to the
drywall when tiling. I dont plan to tile to the ceiling or do a I
plan to tiles the walls outside the shower area.

Do I...
Do I tape and mud the seam where the backer board hits the tile with
tile mastic and then tile slighly over the line with the tiles. In
this example if the backer board goes 6 feet high I would tile up to
say 6 foot 2 or so.

or do I
tape and mud the seam with spackel Coating the top inch or so with
spackel and then tiling up to the 5 foot 10 mark...

I dont know that spackel attaches to backer board so I think the first
choice is right but just wanted to be sure. At first I quickly
thought that you might not want to tile over the drywall backerboard
seam but after thinking about it further I thought that the
backbaord/drywall seam is not really much differnt then tiling over a
backerboard/backerboard seam

Is that right?