Clarify how to add a field to a named tuple.
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index b276ab0..1e213fb 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -538,7 +538,7 @@
Subclassing is not useful for adding new, stored fields. Instead, simply
create a new named tuple type from the :attr:`_fields` attribute::
- >>> Pixel = namedtuple('Pixel', Point._fields + Color._fields)
+ >>> Point3D = namedtuple('Point3D', Point._fields + ('z',))
Default values can be implemented by using :meth:`_replace` to
customize a prototype instance::