3. We drew parallels between 1 atm solvated electrons (and related species) and HPEs, whose electronic structure has been described using models where electrons are confined in voids (within a solvent or a solid), as well as models that involve the formation of multi-centered bonds (MCBs) resulting from orbital overlap. 4. For both classes of electrides the MCB schemes require participation from orbitals that are typically considered unoccupied, whereas the confined-electron (e.g. interstitial quasi-atom, ISQ) type models invoke orbitals that are centered on the voids. 5. Pressure reorders the energy levels of orbitals, so the new valence orbitals can hybridize and participate in MCB schemes.