How to control the ribbon position in XML for Word Web Addin (Using Node.js ie. JavaScript)

Question

Hi,

Does anyone know the equivalent to CustomUI property of  insertAfterIdMso="TabHome" to use in Word Web Addins, i.e. for the XML below, how do I control the posittion of the CustomTab so that it loads after the Home Tab in Word or Excel?

<!-- PrimaryCommandSurface is the main Office Ribbon. -->
          <ExtensionPoint xsi:type="PrimaryCommandSurface">
            <!-- Use OfficeTab to extend an existing Tab. Use CustomTab to create a new tab. -->
  <CustomTab id="MyTab">

Kind regards
Fiona