# Lesson 4 complete; external sources still unread

Learner finished lesson 0004 (indexes, ranges, cursors) and still has **not** read the deferred external primaries (MDN Using IndexedDB, MDN basic terminology, web.dev idb walkthrough). Treat as known from lessons only: indexes are upgrade-time schema; unique/multiEntry options at a glance; index.get/getAll; IDBKeyRange shapes; getAll for modest sets vs openCursor for large/streamed work; index write + version-bump cost. Implementation depth and edge cases from MDN remain open — not assumed. Next ZPD: integration deal-breakers (quota, eviction, multi-tab writers, wrong-tool rejects) toward design-review fluency.