This is an experiment to link an Adobe Photoshop Elements Web Gallery using a Sandvox External Page with the Inspector setting as page-within-page for the external page.
Click image to go to the Gallery
[Adobe Photoshop Elements Web Gallery]
1. I have added a Summaries Collection page and added an External Page page inside it.
2. I have uploaded the Gallery folder created by Abode Photoshop Elements / Bridge using an FTP client to the folder created by Sandvox for the Collection page. (A Collection page is actually a folder with an index.html page inside.)

3. I linked the External Page to the URL for the folder containing the Adobe Web Photo Gallery. The index.html file inside the gallery folder will automatically be shown by a browser.
4. -->In the Inspector for the External Page, I have turned off the sidebar, added a thumbnail, chosen to show page-within-page, left the width at 100% and change the height to 520 pixels
Problem: Sandvox shows the whole external page on the collection index page (i.e. HowTo) regardless of any settings set in the Inspector - NOOOOO!!!
Problem Update: I change this collection folder (Photoshop Elements Gallery Added to Sandvox) to have no index and linked to the External Page (which links to the gallery folder on the web) in the Site Outline from the image and text above.
