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
 
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 4ba6956..0c773da 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -164,10 +164,8 @@
     value = utils.read_only_property("_value")
 
     def __repr__(self):
-        return ("<Extension(oid={oid}, "
-                "critical={critical}, value={value})>").format(
-            oid=self.oid, critical=self.critical, value=self.value
-        )
+        return ("<Extension(oid={0.oid}, critical={0.critical}, "
+                "value={0.value})>").format(self)
 
 
 class BasicConstraints(object):
@@ -191,10 +189,8 @@
     path_length = utils.read_only_property("_path_length")
 
     def __repr__(self):
-        return ("<BasicConstraints(ca={ca}, "
-                "path_length={path_length})>").format(
-            ca=self.ca, path_length=self.path_length
-        )
+        return ("<BasicConstraints(ca={0.ca}, "
+                "path_length={0.path_length})>").format(self)
 
 
 OID_COMMON_NAME = ObjectIdentifier("2.5.4.3")