3GPP 24.501 v20.0.0 — the document's own text
8.2.2.3 EAP message
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
EAP message IE is included if the EAP message received in a related AUTHENTICATION REQUEST message was an EAP-request.