The 'Search in Full Text' option will provide more results by looking for search terms within the entire article or book. 

i.  Search the library catalogue (Primo Library Search)

ii. If you do not want to include these results in your search, you can use the toggle to turn it off.

Please note that although the slider will stay activated for the entirety of the session, it will return to it's original position when the browser is closed or the page is refreshed.