Xenon gas is known for its excellent anesthetic properties and chemical activity. On page 473, Marek Ilczyszyn and Dawid Gąszowski consider properties of complexes formed by Xe atoms and their lighter analogues, Ne, Ar, and Kr, with selected acids of different structures and acidities. Special attention is given to water complexes. Bader's Quantum Theory of Atoms in Molecules is used, and the results are analyzed in relation to the hydrogen bonding criteria developed by Koch and Popelier for classic hydrogen bonds. The concept of the hydrogen bonding interaction is reviewed for these very weak systems.