diff --git a/pcapkit/protocols/internet/ah.py b/pcapkit/protocols/internet/ah.py
index 5546c22c5..11f99570b 100644
--- a/pcapkit/protocols/internet/ah.py
+++ b/pcapkit/protocols/internet/ah.py
@@ -52,11 +52,17 @@ class AH(IPsec[Data_AH, Schema_AH], IPv6_Ext[Data_AH, Schema_AH],
     """This class implements Authentication Header.
 
     Double-inherited (GitHub issue #917): ``AH`` is both a member of the
-    IPsec family and an IPv6 extension header -- IANA's
-    ``protocol-numbers-1.csv`` marks it ``Y`` in the *IPv6 Extension Header*
-    column (:rfc:`4302`), and this package's own
+    IPsec family and an IPv6 extension header -- IANA's *IPv6 Extension
+    Header Types* registry lists it at 51 (:rfc:`4302#section-3.1.1` has
+    it appear after the hop-by-hop, routing and fragmentation extension
+    headers in the IPv6 header chain), and this package's own
     :class:`~pcapkit.const.ipv6.extension_header.ExtensionHeader` registry
-    agrees. :class:`~pcapkit.protocols.internet.ipsec.IPsec` is first in the
+    agrees. The same section separately states that, in the context of
+    IPv4, AH is placed after the IP header and before the next-layer
+    protocol -- the primary-source evidence that it also travels
+    directly as an IPv4 payload, which is what qualifies it for a base
+    besides :class:`~pcapkit.protocols.internet.ipv6_ext.IPv6_Ext`.
+    :class:`~pcapkit.protocols.internet.ipsec.IPsec` is first in the
     bases so that its :meth:`~pcapkit.protocols.internet.ipsec.IPsec.id`
     keeps precedence.
 
diff --git a/pcapkit/protocols/internet/esp.py b/pcapkit/protocols/internet/esp.py
index 88cfcd591..7a1f50585 100644
--- a/pcapkit/protocols/internet/esp.py
+++ b/pcapkit/protocols/internet/esp.py
@@ -976,12 +976,19 @@ class ESP(IPsec[Data_ESP, Schema_ESP], IPv6_Ext[Data_ESP, Schema_ESP],
     """This class implements Encapsulating Security Payload.
 
     Double-inherited (GitHub issue #917), mirroring
-    :class:`~pcapkit.protocols.internet.ah.AH`: IANA's
-    ``protocol-numbers-1.csv`` marks ``ESP`` ``Y`` in the *IPv6 Extension
-    Header* column (:rfc:`4303`), and this package's own
+    :class:`~pcapkit.protocols.internet.ah.AH`: IANA's *IPv6 Extension
+    Header Types* registry lists ``ESP`` at 50 (:rfc:`4303#section-3.1.1`
+    has it appear after the hop-by-hop, routing and fragmentation
+    extension headers in the IPv6 header chain), and this package's own
     :class:`~pcapkit.const.ipv6.extension_header.ExtensionHeader` registry
-    agrees (``ESP = 50``), so it must honour the same extension-mode contract
-    as its siblings. :attr:`payload` and :attr:`protochain` come from
+    agrees (``ESP = 50``), so it must honour the same extension-mode
+    contract as its siblings. The same section separately states that,
+    in the context of IPv4, ESP is placed after the IP header and
+    before the next-layer protocol -- the primary-source evidence that
+    it also travels directly as an IPv4 payload, which is what
+    qualifies it for a base besides
+    :class:`~pcapkit.protocols.internet.ipv6_ext.IPv6_Ext`.
+    :attr:`payload` and :attr:`protochain` come from
     :class:`~pcapkit.protocols.internet.ipv6_ext.IPv6_Ext`; :attr:`protocol`
     is spelled out below for the reason given there.
 
diff --git a/tests/protocols/internet/test_ah_unit.py b/tests/protocols/internet/test_ah_unit.py
index 56330c007..619690b18 100644
--- a/tests/protocols/internet/test_ah_unit.py
+++ b/tests/protocols/internet/test_ah_unit.py
@@ -114,6 +114,76 @@ def test_ah_read_properties_and_ipsec_id(self) -> None:
         self.assertTrue(post_proto._extf)
         post_init.assert_called_once()
 
+    def test_docstring_cites_the_extension_header_registry(self) -> None:
+        """GitHub issue #931.
+
+        The class docstring's extension-header *membership* claim must
+        rest on IANA's authoritative *IPv6 Extension Header Types*
+        registry (and this package's own registry, generated from it),
+        not the ``protocol-numbers-1.csv`` *IPv6 Extension Header* column
+        that #926 repointed the const generator away from -- that column
+        is a derived signal, not the registry :rfc:`8200#section-4` names
+        as authoritative, and disagreed with it on header 147
+        (``BIT_EMU``).
+
+        :rfc:`4302#section-3.1.1` is cited too, but only for what it
+        actually says: an IPv6-context placement recommendation ("should
+        appear after hop-by-hop, routing, and fragmentation extension
+        headers"), not a membership assertion -- membership is the
+        registry's claim, per
+        ``docs/source/contributing/conventions.rst``'s "being *in* that
+        registry is what makes something an extension header" ruling.
+        Rephrasing the placement sentence as "places it among the IPv6
+        extension headers" overstated the RFC; that was caught in review
+        on the second version of this fix.
+
+        The section's separate IPv4-context sentence ("placed after the
+        IP header ... before the next layer protocol") is legitimate
+        prose here too -- it is the primary-source evidence that AH
+        also travels directly as an IPv4 payload, exactly as
+        :mod:`~pcapkit.protocols.internet.hip` cites its own IPv4
+        appendix for the same reason. Per
+        ``docs/source/contributing/conventions.rst``'s "own-protocolhood
+        on its own is not sufficient" ruling (MH is the settling case),
+        that fact *qualifies* an already-standalone header for a base
+        besides :class:`~pcapkit.protocols.internet.ipv6_ext.IPv6_Ext`;
+        it does not *make* the header standalone, and the RFC has no
+        say in which base is named. An earlier revision of this
+        docstring's ``ESP`` counterpart claimed the RFC "makes it a
+        standalone protocol" and "names ``IPsec`` as the second base",
+        the latter positionally false and unsupported by the cited
+        section; both were caught in review on the third version of
+        this fix. So this test targets the exact wrong phrasing from
+        the earlier rounds rather than banning "IPv4" outright, which
+        would forbid the legitimate use kept above.
+        """
+        import re
+
+        from pcapkit.protocols.internet.ah import AH
+
+        # Normalise the docstring's line-wrapping before matching, since the
+        # citation may be split across lines by hand-wrapping.
+        doc = ' '.join((AH.__doc__ or '').split())
+        self.assertNotIn('protocol-numbers-1.csv', doc)
+        self.assertNotIn('among the IPv6 extension headers', doc)
+        self.assertNotIn('second base', doc)
+        self.assertNotIn('directly after an IPv4 header', doc)
+
+        # Pin the claim, not just the phrase: whatever the RFC-placement
+        # parenthetical attached directly to the registry-membership
+        # sentence says, it must not smuggle in IPv4 evidence for that
+        # claim, regardless of how a future revision words it.
+        membership_clause = re.search(r'registry lists it at 51 \((.*?)\)', doc)
+        self.assertIsNotNone(membership_clause, 'could not locate the membership clause')
+        self.assertNotIn('IPv4', membership_clause.group(1))
+
+        self.assertIn('IPv6 Extension Header Types', doc)
+        self.assertIn(':rfc:`4302#section-3.1.1`', doc)
+        self.assertIn('hop-by-hop, routing and fragmentation', doc)
+        self.assertIn('IPv6 header chain', doc)
+        self.assertIn('travels directly as an IPv4 payload', doc)
+        self.assertIn('qualifies it for a base besides', doc)
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/tests/protocols/internet/test_esp_unit.py b/tests/protocols/internet/test_esp_unit.py
index 4f4ad5970..995420c32 100644
--- a/tests/protocols/internet/test_esp_unit.py
+++ b/tests/protocols/internet/test_esp_unit.py
@@ -1038,6 +1038,79 @@ def test_ipv6_extension_header_position(self) -> None:
         self.assertIn(str(ESP.__index__()), [str(key) for key in ipv6.extension_headers])
         self.assertIn('ESP', str(ipv6.protochain))
 
+    def test_docstring_cites_the_extension_header_registry(self) -> None:
+        """GitHub issue #931.
+
+        The class docstring's extension-header *membership* claim must
+        rest on IANA's authoritative *IPv6 Extension Header Types*
+        registry (and this package's own registry, generated from it),
+        not the ``protocol-numbers-1.csv`` *IPv6 Extension Header* column
+        that #926 repointed the const generator away from -- that column
+        is a derived signal, not the registry :rfc:`8200#section-4` names
+        as authoritative, and disagreed with it on header 147
+        (``BIT_EMU``).
+
+        :rfc:`4303#section-3.1.1` is cited too, but only for what it
+        actually says: an IPv6-context placement recommendation ("should
+        appear after hop-by-hop, routing, and fragmentation extension
+        headers"), not a membership assertion -- membership is the
+        registry's claim, per
+        ``docs/source/contributing/conventions.rst``'s "being *in* that
+        registry is what makes something an extension header" ruling.
+        Rephrasing the placement sentence as "places it among the IPv6
+        extension headers" overstated the RFC and contradicted this same
+        docstring's ``Note:`` (which says RFC 8200 declines ESP
+        extension-header status); that was caught in review on the
+        second version of this fix.
+
+        The section's separate IPv4-context sentence ("placed after the
+        IP header ... before the next layer protocol") is legitimate
+        prose here too -- it is the primary-source evidence that ESP
+        also travels directly as an IPv4 payload, exactly as
+        :mod:`~pcapkit.protocols.internet.hip` cites its own IPv4
+        appendix for the same reason. Per
+        ``docs/source/contributing/conventions.rst``'s "own-protocolhood
+        on its own is not sufficient" ruling (MH is the settling case),
+        that fact *qualifies* an already-standalone header for a base
+        besides :class:`~pcapkit.protocols.internet.ipv6_ext.IPv6_Ext`;
+        it does not *make* the header standalone, and the RFC has no
+        say in which base is named (``IPsec`` versus ``Internet``) --
+        an earlier revision claimed the RFC "makes it a standalone
+        protocol" and "names ``IPsec`` as the second base", the latter
+        positionally false (``ESP.__bases__`` puts ``IPsec`` first, not
+        second) and unsupported by the cited section; both were caught
+        in review on the third version of this fix. So this test
+        targets the exact wrong phrasing from the earlier rounds rather
+        than banning "IPv4" outright, which would forbid the legitimate
+        use kept above.
+        """
+        import re
+
+        from pcapkit.protocols.internet.esp import ESP
+
+        # Normalise the docstring's line-wrapping before matching, since the
+        # citation may be split across lines by hand-wrapping.
+        doc = ' '.join((ESP.__doc__ or '').split())
+        self.assertNotIn('protocol-numbers-1.csv', doc)
+        self.assertNotIn('among the IPv6 extension headers', doc)
+        self.assertNotIn('second base', doc)
+        self.assertNotIn('directly after an IPv4 header', doc)
+
+        # Pin the claim, not just the phrase: whatever the RFC-placement
+        # parenthetical attached directly to the registry-membership
+        # sentence says, it must not smuggle in IPv4 evidence for that
+        # claim, regardless of how a future revision words it.
+        membership_clause = re.search(r'registry lists ``ESP`` at 50 \((.*?)\)', doc)
+        self.assertIsNotNone(membership_clause, 'could not locate the membership clause')
+        self.assertNotIn('IPv4', membership_clause.group(1))
+
+        self.assertIn('IPv6 Extension Header Types', doc)
+        self.assertIn(':rfc:`4303#section-3.1.1`', doc)
+        self.assertIn('hop-by-hop, routing and fragmentation', doc)
+        self.assertIn('IPv6 header chain', doc)
+        self.assertIn('travels directly as an IPv4 payload', doc)
+        self.assertIn('qualifies it for a base besides', doc)
+
 
 if __name__ == '__main__':
     unittest.main()