diff --git a/force_bdss/base_extension_plugin.py b/force_bdss/base_extension_plugin.py
index 28c543d080387a3880579f67ce3c4aa44d2de50f..3627b137961a3dcea0fb44068d42abdcdd5e08e3 100644
--- a/force_bdss/base_extension_plugin.py
+++ b/force_bdss/base_extension_plugin.py
@@ -8,17 +8,33 @@ from force_bdss.mco.i_multi_criteria_optimizer_bundle import \
 
 
 class BaseExtensionPlugin(Plugin):
+    """Base class for extension plugins, that is, plugins that are
+    provided by external contributors.
+
+    It provides a set of slots to be populated that end up contributing
+    to the application extension points. To use the class, simply inherit it
+    in your plugin, and then define the trait default initializer for the
+    specific trait you want to populate. For example::
+
+        class MyPlugin(BaseExtensionPlugin):
+            def _data_source_bundles(self):
+                return [MyDataSourceBundle1(),
+                        MyDataSourceBundle2()]
+    """
+
+    #: A list of available Multi Criteria Optimizers this plugin exports.
     mco_bundles = List(
         IMultiCriteriaOptimizerBundle,
         contributes_to='force.bdss.mco.bundles'
     )
 
-    #: A list of the available Data Sources.
-    #: It will be populated by plugins.
+    #: A list of the available Data Sources this plugin exports.
     data_source_bundles = List(
         IDataSourceBundle,
-        contributes_to='force.bdss.data_sources.bundles')
+        contributes_to='force.bdss.data_sources.bundles'
+    )
 
+    #: A list of the available KPI calculators this plugin exports.
     kpi_calculator_bundles = List(
         IKPICalculatorBundle,
         contributes_to='force.bdss.kpi_calculators.bundles'