diff --git a/runtime/doc/vim9class.txt b/runtime/doc/vim9class.txt
index 6b51e86..0660254 100644
--- a/runtime/doc/vim9class.txt
+++ b/runtime/doc/vim9class.txt
@@ -530,6 +530,10 @@
 set to "any" during class definition.  When an object is instantiated from the
 class, then the type of the variable is set.
 
+The following reserved keyword names cannot be used as an object or class
+variable name: "super", "this", "true", "false", "null", "null_blob",
+"null_dict", "null_function", "null_list", "null_partial", "null_string",
+"null_channel" and "null_job".
 
 Extending a class ~
 							*extends*
@@ -543,9 +547,11 @@
 is not possible to override them (unlike some other languages).
 
 						*E1356* *E1357* *E1358*
-Object methods of the base class can be overruled.  The signature (arguments,
-argument types and return type) must be exactly the same.  The method of the
-base class can be called by prefixing "super.".
+Object methods of the base class can be overruled.  The number of arguments
+must be exactly the same.  The method argument type can be a contra-variant
+type of the base class method argument type.  The method return value type can
+be a covariant type of the base class method return value type.  The method of
+the base class can be called by prefixing "super.".
 
 						*E1377*
 The access level of a method (public or private) in a child class should be