PEP 484: Clarify scoping of type variables (#231)

pep-0484.txt

@@ -472,9 +472,9 @@ However, there are some special cases in the static typechecking context:
     def fun_2(x: T) -> T: ... # and here could be different
 
     fun_1(1)                  # This is OK, T is inferred to be int
-    fun_2('a')                # This is aslo OK, now T is str
+    fun_2('a')                # This is also OK, now T is str
 
-* A type variable used in a method of a generic class that coincisides
+* A type variable used in a method of a generic class that coincides
   with one of the variables that parameterize this class is always bound
   to that variable. Example::
 
@@ -537,8 +537,22 @@ However, there are some special cases in the static typechecking context:
         class MyGeneric(Generic[T]):
             ...
 
-* A generic class nested in another generic class cannot use the same
-  type variables, unless the inner class definition is inside a function.
+* A generic class nested in another generic class cannot use same type
+  variables. The scope of the type variables of the outer class
+  doesn't cover the inner one::
+
+    T = TypeVar('T')
+    S = TypeVar('S')
+
+    class Outer(Generic[T]):
+        class Bad(Iterable[T]):      # Error
+            ...
+        class AlsoBad:
+            x = None # type: List[T] # Also an error
+
+        class Inner(Iterable[S]):    # OK
+            ...
+        attr = None # type: Inner[T] # Also OK
 
 
 Instantiating generic classes and type erasure