Add a sentence clarifying that once a path_hooks importer has

been found for a sys.path entry, the builtin import machinery will not
handle that entry any longer.

pep-0302.txt

@@ -311,13 +311,16 @@ Specification part 2: Registering Hooks
     sequence to determine if they can handle a given path item.  The
     callable is called with one argument, the path item.  The callable
     must raise ImportError if it is unable to handle the path item, and
-    return an importer object if it can handle the path item.  The
+    return an importer object if it can handle the path item.  Note
-    callable is typically the class of the import hook, and hence the
+    that if the callable returns an importer object for a specific
-    class __init__ method is called.  (This is also the reason why it
+    sys.path entry, the builtin import machinery will not be invoked
-    should raise ImportError: an __init__ method can't return anything.
+    to handle that entry any longer, even if the importer object later
-    This would be possible with a __new__ method in a new style class,
+    fails to find a specific module.  The callable is typically the
-    but we don't want to require anything about how a hook is
+    class of the import hook, and hence the class __init__ method is
-    implemented.)
+    called.  (This is also the reason why it should raise ImportError:
+    an __init__ method can't return anything.  This would be possible
+    with a __new__ method in a new style class, but we don't want to
+    require anything about how a hook is implemented.)
 
     The results of path hook checks are cached in
     sys.path_importer_cache, which is a dictionary mapping path entries