XML Schemas

Validating XML Editor (customui.xsd)

The quickest way to create RibbonX markup is to use an XML Editor and provide it with the necessary XSD schema
The schema can be obtained by searching for Office 2007 XML schema reference

You need to open your office document (.xlsm, .docm)
If this file contains any custom UI then a customUI.xml file will appear underneath the office document
SS

Office 2007 - customUI.xml
Office 2010 - customUI14.xml - adds ActivateTab, ActivateTabMso, ActivateTabQ - also adds autoscale, centervertically, getImage, image, imageMso attributes for groups ?

xmlns Reference
2010 - http://schemas.microsoft.com/office/2009/07/customui
2007 - http://schemas.microsoft.com/office/2006/01/customui

Intellisense

You can enable intellisense for the XML markup to help reduce the typing errors.
Microsoft provides a schema for the Ribbon called CustomUI.xsd that you can reference in your add-in and enable intellisense for the XML markup.
You can find this schema by searching MSDN for "2007 Office System XML Schema".

Save this file in
\Program Files\Microsoft Visual Studio\8\XML\Schemas\
and add a reference to the file in your Project properties

This will give you intellisense drop-down and displays all the attributes available for a particular control.