See
Section 1
from Theory document for mathematical definition.
B:
Bilinear
F:
Linear
Q:
Quadratic
Tr:
Threelinear
TrQB:
Threelinear-Quadratic-Bilinear
TrB:
Threelinear-Bilinear
TrF:
Threelinear-Linear
TrC:
Threelinear-Cubic