Top 2 layers of a regression tree trained with combination of all tables, except 1c9oA. The actual tree contains 55 nodes. Each path from the root to a node defines a conjunction of criteria for H-bonds with a certain mean stability. Here, Dist_H_A (the distance between the hydrogen and the acceptor atoms) is the most differentiating predictor. For H-bonds with Dist_H_A≥2.40Å, the mean stability is only 0.38, but it increases to 0.92 if Dist_H_A<2.40Å.