Interactive pictures question

If you look at the free iBook "Life on Earth" that's in the new textbook section of the bookstore, you will find that when you tap pictures or do a two finger spread, they enlarge to full screen mode. Is this some special widget that the publisher has or can you do this with iBooks Author's standard widgets? After a lot of searching on the internet, I discovered that you can get pictures to enlarge with a tap by selecting the picture and then in the Widget Inspector clicking the title selection under layout followed by clicking the Full screen only selection under Interactive. This essentially turns the selected picture into a one picture gallery to which you can add a caption if so desired. If you do this, the picture will enlarge to its full size when taped on your ipad. However, this does not do the two finger spread enlargement mentioned above. You can enlarge the image by spreading your fingers on the iPad screen, but as soon as you remove your fingers the picture pops back to it's original size on the page. In "Life on Earth" it will stay at its enlarged size when you remove your fingers.

And yes, I have looked at Publishing with iBooks Author, but have not been able to find anything about the question above.

Thanks for any insight.