Mathematic algorithm used in Stacking Sequence Optimization (Shuffling Phase)

Hello, good afternoon. I am conducting a three-phase optimization for composite material structures using Altair:
.According to OptiStruct, the default optimization methods for free-size and size parameters are the DUAL2 optimization method (based on the CONLIN algorithm) and the MFD method, respectively. However, despite my research, I haven't found which mathematical optimization method is used for the Shuffling phase (Stacking Sequence Optimization). I would venture to say that OptiStruct executes a branch and bound approach based on the optimization data.
More specifically, in the third phase, I am performing a MINMAX optimization, using Tsai-Hill both as the objective function to minimize and as a constraint function (not exceeding a Tsai-Hill value of 1).
What do you think? Is Branch & Bound the default method in the shuffling phase?