Fix documentation.

[skip ci]

docs/usage/basic_usage.rst

@@ -103,9 +103,11 @@ properly.
 To use classes in Python 3
     ``__metaclass__`` must be set. Set it to ``type`` to use no custom metaclass.
 
-To use ``for`` statements and comprehensions
-    ``_getiter_`` must point to :func:`RestrictedPython.Eval.default_guarded_getiter` and
-    ``_iter_unpack_sequence_`` must point to :func:`RestrictedPython.Guards.guarded_iter_unpack_sequence`.
+To use ``for`` statements and comprehensions:
+    * ``_getiter_`` must point to an ``iter`` implementation. As an unguarded variant you might use 
+       :func:`RestrictedPython.Eval.default_guarded_getiter`.
+
+    *  ``_iter_unpack_sequence_`` must point to :func:`RestrictedPython.Guards.guarded_iter_unpack_sequence`.
 
 To use ``getattr``
     you have to provide an implementation for it.