> If I use C-x C-t, the cursor goes down, while the line goes up. I cannotWhich line? Obviously one line is moving down if another is moving up.
> move the line the second time.
If you want point to move along with the upward-moving line rather than
the downward-moving one, use C-- C-x C-t (and then C-x z z ... as needed).
What's the difference?
> And this only transposes the line, not move the line.