diff --git a/skimage/viewer/widgets/core.py b/skimage/viewer/widgets/core.py
index 23bc46b7..826dc4f5 100644
--- a/skimage/viewer/widgets/core.py
+++ b/skimage/viewer/widgets/core.py
@@ -2,8 +2,12 @@
 Widgets for interacting with ImageViewer.
 
 These widgets should be added to a Plugin subclass using its `add_widget`
-method. The Plugin will delegate action based on the widget's parameter type
-specified by its `ptype` attribute, which can be:
+method or calling::
+
+    plugin += Widget(...)
+
+on a Plugin instance. The Plugin will delegate action based on the widget's
+parameter type specified by its `ptype` attribute, which can be:
 
     'arg' : positional argument passed to Plugin's `filter_image` method.
     'kwarg' : keyword argument passed to Plugin's `filter_image` method.