Do it yourself

First of all, thank you to David and Shane for your previous answers to my tile questions. I have another tile question. I am tiling the surround of my bathtub which previously had no surround as it only had a tub faucet and no shower. I have installed the new valve for the shower head and will tile the entire surround. On the back wall is a window. My question is what is the proper method of tiling around the window. Do I remove the casing and tile up to the window, or do I tile around the window casing. If I do the later, will there be any risk of wicking? Hopefully, my above explanation is understandable. Thanks for any advise and opinions. Regards, Eric. . .