Added useful comment

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56020 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/propgrid/propgrid.cpp

@@ -3636,6 +3636,12 @@ bool wxPropertyGrid::DoSelectProperty( wxPGProperty* p, unsigned int flags )
                                                                 goodPos,
                                                                 grect.GetSize());
 
+                //
+                // Below, bear in mind the difference between primaryCtrl and m_wndEditor:
+                // m_wndEditor is the actual wxWindow on canvas, and primaryCtrl is
+                // the actual editor control. They may different if wxPGClipperWindow is
+                // used for this editor.
+                //
                 m_wndEditor = wndList.m_primary;
                 m_wndEditor2 = wndList.m_secondary;
                 wxWindow* primaryCtrl = GetEditorControl();