In case you haven't noticed: if you modify the Ribbon and think your modifications are fine by attaching to RegistrationID 101 (Document Library) then you won't have them show up for the Site Assets library, which has its own RegistrationID of 851.

 

I couldn't find the msdn entry for it. I am sure it's there as documentation is supposed to be sooo much better for SP 2010 (pun intended ;-)

 

Well, once I had the RegistrationID and did a search specifically for it I found 1 (ONE) page that had this info and also a comprehensive list for RegistrationID's: "Mike Smith's Tech Training Notes".

 

I love the SharePoint community! Otherwise half the solutions out there wouldn't exist.