The search button will open the playlists menus, such that the top section is open and the ‘All Songs’ playlist is selected. In this top section there is also the ‘Recent’ playlist. These two lists are derived, you cannot edit them. All Songs contains a reference to all songs in all of the playlists present in the app currently. Remember, the search field will run the search as you type in, but only on the selected playlist. So, if you want all songs in all playlists searched, be sure to select the ‘All Songs’ playlist first, then type into the search field.