OK, I figured out a little bit about the Pages (not tabs).
Default, is the background page, and everything placed on Default will display on every page.
Changing pages from a button is actually very easy.
Add multiple pages, and when you add a button, and click on its Events (lightning bolt), there's a GoTo Page option, which lets you select the page to go to.
I don't know the Lua call to change pages, which I think Terry's looking for?