Custom UI Editor - how do I add a group to tab created in a different workbook ?

[pplanch]

I just started with Office Ribbon Editor to include a custom tab on my ribbon. The idea is to have buttons from various workbooks (later to be converted to add-ins) on the SAME custom tab.

The creation of the tab with the first button group worked fine ... see XML code below :

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customUI xmlns=(note this is redacted because the forum apparently denies posts with URL's in them ... it contains the URL to the 2006-01 custom schemas)>
<ribbon>
<tabs>
<tab id="piAddIns" label="pi Add-ins" insertAfterMso="TabHome" >
<group id="piGeneralSettings" label="General Settings" >
<button id="piRegistration" label="Registration" size="large" onAction="UpdateRegistrationSettings" imageMso="AccountSettings" />
<button id="piLanguage" label="Language" size="large" onAction="SelectLanguage" imageMso="MailMergeRecepientsUseOutlookContacts" />
</group>
</tab>
</tabs>
</ribbon>
</customUI>

The problem I have is to then in ANOTHER workbook add XML code that will add that workbook's button to this "new" tab that I just created (called "piAddIns"). I tried XML code below (with variants of id, idQ and idMSO) to no avail. If I could get some help to figure this out (or pointers to what I'm doing wrong), that would be fantastic ...

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customUI xmlns= (note this is redacted because the forum apparently denies posts with URL's in them)>
<ribbon>
<tabs>
<tab idQ="piAddIns" label="pi Add-ins" >
<group id="piDatePicker" label="Date Picker" insertAfterQ="piGeneralSettings" >
<button id="piPickDate" label="Pick a Date" size="large" onAction="DatePickerMacro" imageMso="CalendarsGallery" />
</group>
</tab>
</tabs>
</ribbon>
</customUI>