Fix _container -> _layer_artist_container in docs

doc/customizing_guide/full_custom_qt_viewer.rst

@@ -204,7 +204,7 @@ the apparance of the layer as necessary before redrawing.
 
 In the data viewer, when the user adds a dataset or a subset, the list of
 layers should then be updated. The layers are kept in a list in the
-``_container`` attribute of the data viewer, and layers can be added and
+``_layer_artist_container`` attribute of the data viewer, and layers can be added and
 removed with ``append`` and ``remove`` (both take one argument, which is a
 specific layer artist). So when the user adds a dataset, the viewer should do
 something along the lines of:
@@ -215,4 +215,4 @@ something along the lines of:
 
 If the user removes a layer from the list of layers by e.g. hitting the
 backspace key, the ``clear`` method is called, followed by the ``redraw``
-method.
+method.