Document custom key completions

docs/source/config/integrating.rst

@@ -1,44 +1,52 b''
 .. _integrating:
 
 =====================================
 Integrating your objects with IPython
 =====================================
 
 Tab completion
 ==============
 
 To change the attributes displayed by tab-completing your object, define a
 ``__dir__(self)`` method for it. For more details, see the documentation of the
 built-in `dir() function <http://docs.python.org/library/functions.html#dir>`_.
 
+You can also customise key completions for your objects, e.g. pressing tab after
+``obj["a``. To do so, define a method ``_ipython_key_completions_()``, which
+returns a list of objects which are possible keys in a subscript expression
+``obj[key]``.
+
+.. versionadded:: 5.0
+   Custom key completions
+
 Rich display
 ============
 
 The notebook and the Qt console can display richer representations of objects.
 To use this, you can define any of a number of ``_repr_*_()`` methods. Note that
 these are surrounded by single, not double underscores.
 
 Both the notebook and the Qt console can display ``svg``, ``png`` and ``jpeg``
 representations. The notebook can also display ``html``, ``javascript``,
 and ``latex``. If the methods don't exist, or return ``None``, it falls
 back to a standard ``repr()``.
 
 For example::
 
     class Shout(object):
         def __init__(self, text):
             self.text = text
         
         def _repr_html_(self):
             return "<h1>" + self.text + "</h1>"
 
 Custom exception tracebacks
 ===========================
 
 Rarely, you might want to display a different traceback with an exception -
 IPython's own parallel computing framework does this to display errors from the
 engines. To do this, define a ``_render_traceback_(self)`` method which returns
 a list of strings, each containing one line of the traceback.
 
 Please be conservative in using this feature; by replacing the default traceback
 you may hide important information from the user.