Pure-reference catalog of PCI DSS v4.0 scope reduction techniques + the testable scope boundaries. Covers the SAQ levels (A through D, picked by how cardholder data flows), the PAN-storage prohibitions (only first-6 + last-4 retained; nothing else cleartext), the tokenization + hosted-fields scope-reduction patterns (Stripe Elements / Adyen Drop-in / Braintree Hosted Fields keep PAN off your servers), Network-Segmentation as PCI scope-reduction, and the testable behaviours the scope boundary creates. This is the catalog of WHY the boundary matters and what it makes testable - not a checker that verifies a given integration against the standard. Use when designing or auditing the PCI scope of a payment integration.