the Help File doesn't cover what these radio buttons do for Search and Replace (IDE).
What does All Projects vs. Current Project do? Is it referring to Action Lists? Or will it actually search all Projects you have associated via "Include Project"?
That is correct. You can do a search and replace across all open projects if you wish. Also note that it also applies to searching itself. Typically I leave this to just a single project just to make thought processes simpler for myself.