Merge pull request #839 from CadQuery/marcus7070/introspective-example-note

doc/primer.rst: introspective example additional note

Author: jmwright

doc/primer.rst

@@ -560,14 +560,14 @@ another :class:`~cadquery.Workplane` method).
 
 The next step is to extrude this circle and create a cylindrical protrusion::
 
-    part = part.extrude(1)
+    part = part.extrude(1, clean=False)
 
 Now:
 
 .. code-block:: none
 
     Workplane object at 0xafd0:
-      parent: Workplane object at 0x6df0
+      parent: Workplane object at 0xe790
       plane: Plane object at 0x3e80:
         origin: (0.5, 0.0, 0.0)
         z direction: (1.0, 0.0, 0.0)
@@ -582,6 +582,16 @@ The :meth:`~cadquery.Workplane.extrude` method has cleared all the pending wires
 that is shown in the 3D view above.
 
 
+.. note::
+  The :meth:`~cadquery.Workplane.extrude` has an argument for ``clean`` which defaults to ``True``.
+  This extrudes the pending wires (creating a new :class:`~cadquery.Workplane` object), then runs
+  the :meth:`~cadquery.Workplane.clean` method to refine the result, creating another
+  :class:`~cadquery.Workplane`. If you were to run the example with the default
+  ``clean=True`` then you would see an intermediate
+  :class:`~cadquery.Workplane` object in :attr:`~cadquery.Workplane.parent`
+  rather than the object from the previous step.
+
+
 Assemblies
 ----------