This file is responsible for bonus priests (clerics and druids) spells because of their wisdom:
Columns numerated from 1 to 7 indicates the priest spell book level.
First column is the CRE's wisdom.
The crossing of them indicate how many bonus spells have priest creature with specified wisdom.

In PSTEE we have:

2DA V1.0
0
        1   2   3   4   5   6   7
13      1   0   0   0   0   0   0
14      2   0   0   0   0   0   0
15      2   1   0   0   0   0   0
16      2   2   0   0   0   0   0
17      2   2   1   0   0   0   0
18      2   2   1   1   0   0   0
19      3   2   2   1   0   0   0
20      3   3   2   2   0   0   0
21      3   3   3   2   1   0   0
22      3   3   3   3   2   0   0
23      4   3   3   3   2   1   0
24      4   3   3   3   3   2   0
25      4   3   3   3   3   3   1