3GPP 23.501 v20.2.0 — the document's own text
5.4.1 UE reachability in CM-IDLE
Taught in 9. Registration, reachability and paging (The 5G system architecture, in depth), 10. Radio, Wi-Fi, cable — every way in (The 5G system architecture, in depth), 4. Knowing who you are and where you are (The 5G system architecture, overview).
This clause has no text of its own; it only holds the clauses below.