I have a RibbonX customization for Excel. It's quite simple and it
works fine... But, I'm trying to make the buttons that I have behave
like the controls in Excel such that when there is no Workbook visible
in Excel I want to disable the buttons.

It appears that I want to invalidate my buttons and call the "enabled"
dynamic attribute, but I can't figure out 2 things:

1. How to recognize that the Excel Workspace has no visible
Workbooks, and
2. Where to put the code the will recognize when a Workbook has been
closed or hidden so that I can do the test in #1 and respond
accordingly.

Thanks for the help!!