I am attempting to use Glade 3.x and the GtkExtra package under Windows.  I added the "gtk+extra-catalog.xml" to my catalog directory under my GTK+ install "C:\Gtk+\share\glade3\catalogs".  I found I have to modify the "gtk+extra-catalog.xml" file to get the gtkExtra widgest to appear in the Glade tool Palette by adding a "parent=" field to the glade-widget-class for example:
<glade-widget-class name="GtkCharSelection" parent="GtkDrawingArea" generic-name="gtkcharselection" title="GtkCharSelection - a widget which contains all the characters in a font"/>
without the addition of the  parent="GtkDrawingArea" field, the widget will not show in the Glade tool palatte.  I am not sure what the correct parent selection for all the class names GtkSheet, GtkSheetColumn, GtkCheckItem, etc..  Or am I going about this wrong ?  Where can I find this information? Why is it not already in the xml file? Without a "parent=" field nothing shows up in Glade.  I have been guessing to what the proper parent should be for each of the widget classes.