When the user wants to implement a custom branch-and-bound algorithm — designing bounding functions, branching rules, node selection (depth-first vs best-first), dominance rules, and incumbent management — or to decide when custom B&B beats a MIP solver. Also use when the user mentions "custom branch and bound," "bounding function," "branching rule," "node selection," "best-first search," or when the bounding relaxation is combinatorial rather than an LP. For solver-internal B&B and MIP gaps, see integer-programming-techniques; for branch-and-price trees, see column-generation.
