Why am I given three choices when merging between my code and someone else's? Shouldn't there just be my code, the other person's code, and the output below? The documentation for KDIFF doesn't help me understand.
A refers to the version your merge target is based on. If you Merge from branch to trunk, 'A' will be the previous trunk version.
B is what you currently have in your local trunk folder, including local changes.
C is the Version you wanna merge on top of B.