some issues about the neighbor rule

when I write my neighbor part(in the sample.xml),I found i couldn't define upper or below neighbor rule. As an example, there is 'T',I want 'T' below neighbor a 'I'. How can i do it?

Indeed, it is only possible to specify left and right neighbors in the xml file. But you still can specify arbitrary adjacencies, because you can rotate the tiles. For example,

<neighbor left="cliff 1" right="road 3"/>

means that the cliff tile rotated 1*90 degrees can be adjacent from the left to the road tile rotated 3*90 degrees. So it is possible to specify vertical adjacencies using tile rotations.

I found these code seem to decide the "upper or below" rules int L = action[firstOccurrence[left[0]]][left.Length == 1 ? 0 : int.Parse(left[1])], D = action[L][1]; int R = action[firstOccurrence[right[0]]][right.Length == 1 ? 0 : int.Parse(right[1])], U = action[R][1]; why the D and U directly use '1' as the second number in the action[][]?

Because Down and Up correspond to Left and Right by rotating 1*90 degrees.