- update to reflect that base classes can be class types as well as

"classic" class objects
  [partially fixes SF bug #453684]

- add note that new-style classes can use descriptors to implement
  instance variables in different ways

Doc/ref/ref7.tex

@@ -419,7 +419,8 @@ A class definition defines a class object (see section~\ref{types}):
 
 A class definition is an executable statement.  It first evaluates the
 inheritance list, if present.  Each item in the inheritance list
-should evaluate to a class object.  The class's suite is then executed
+should evaluate to a class object or class type which allows
+subclassing.  The class's suite is then executed
 in a new execution frame (see section~\ref{naming}), using a newly
 created local namespace and the original global namespace.
 (Usually, the suite contains only function definitions.)  When the
@@ -433,7 +434,7 @@ class object in the original local namespace.
 \indexii{name}{binding}
 \indexii{execution}{frame}
 
-\strong{Programmer's note:} variables defined in the class definition
+\strong{Programmer's note:} Variables defined in the class definition
 are class variables; they are shared by all instances.  To define
 instance variables, they must be given a value in the
 \method{__init__()} method or in another method.  Both class and
@@ -441,3 +442,5 @@ instance variables are accessible through the notation
 ``\code{self.name}'', and an instance variable hides a class variable
 with the same name when accessed in this way.  Class variables with
 immutable values can be used as defaults for instance variables.
+For new-style classes, descriptors can be used to create instance
+variables with different implementation details.