Thanks for your response, Conjurer.
I should probably have been more specific in my initial post, in that I'm using Excel 365 under Windows 10, so am using the Office 2010 Custom UI (although I'm not sure if that makes a difference - but the structure of your list looks more like the items on the old menu bar rather than the ribbon).
I'm not sure how to use a code such as 30010 in place of a word in the Tab line of the UI Editor. I'm currently using <tab id="StellarTab" label="Stellar" insertAfterMso="TabDeveloper"> but would prefer something that translates to <insertBeforeMso="TabHelp"> in order to insert the tab specifically before Help rather than after Developer. This is because the Stellar tab is in an .xlam loaded from the XLStart folder, but I also have a couple of other files that load their own tabs, which I would like to position between the Stellar tab and Help.
Sadly, "TabHelp" achieves nothing.
The problem is that the Stellar tab loads first, then the tab for the next file I open is positioned after the Developer tab but before the Stellar tab. My only other option is to place it right at the end of the toolbar, but I'd really prefer Help to be at the end in all instances. I've tried playing with the idQ option to specify the Stellar tab, but with even less success as there seems to be an even bigger gap in the available information!
I realise words such as TabDeveloper are probably constants representing numbers, but don't know how to tell the UI editor that I'm substituting "TabDeveloper" with the value 30010 for Help. If I enclose the number within inverted commas it doesn't work, which is what I would expect. But if I omit the inverted commas, the label "insertAfterMSO" turns from red to blue, and the custom ribbon tab isn't recognised at all. Both options fail the Validator.
So the simplest solution would be if I could find a reference that tells me what the correct word is for the Help tab, as TabDeveloper is for the Developer tab. Failing that, how to substitute a value in place of a constant.
Cheers
Alison C