[Question] What is AABB6 and BVHNode6 in "aabb.h" and "edge_tree.h" used for?

I want to know how redner is implemented and wander what are d_min and d_max in AABB6 is used for. Are they used for storing differentiation of p_min and p_max?

Another question is an AABB box containing an edge's two points as a leaf BVH node and the ray intersect with the leaf BVH node's AABB box means hitting the edge?