The subject of mixed-valence charge segregation in HTSC materials is further examined. The self-organized microstructural details are explored including 1D/2D crossover. Neutron and extended x-ray absorption fine-structure results provide the basis for this analysis. The Jahn-Teller effect is seen as a crucial element in the `charge/spin'-separation structuring. On cooling, the emergent resonating-valence-bond-type magnetic organization of the divalent subsystem assists greatly in preparing (if not pre-pairing) the overall system for high-temperature superconductivity. Under the action of the negative-U centres of the high-valence subsystem established in the domain boundaries, the system can evolve naturally with doping and cooling from towards greater s-wave-type content of the HTSC order parameter.