doc updates and simplification of __repr__
diff --git a/docs/x509.rst b/docs/x509.rst
index 751e077..36e9fab 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -284,13 +284,16 @@
:type: :class:`ObjectIdentifier`
- The attribute OID.
+ The extension OID.
.. attribute:: critical
:type: bool
- Determines whether a given extension is critical or not.
+ Determines whether a given extension is critical or not. :rfc:`5280`
+ requires that "A certificate-using system MUST reject the certificate
+ if it encounters a critical extension it does not recognize or a
+ critical extension that contains information that it cannot process".
.. attribute:: value