Thumbnail Indexes are Galleries that are automatically filled with a linked selection of pages from your site. To add an index to a page, click the “Add...” button in the top menu bar and choose “Thumbnail Index”.
Since Indexes are galleries, configuring them is mostly the same process but Indexes feature additional options for choosing and styling their contents.
Filtering
In its default state, the Thumbnail Index will display all of the pages in your site. You can change which pages are displayed by opening the settings menu (click the Thumbnail Index button when hovering over the element) and choosing an option from the "Filter by" menu at the top. There are two main ways to filter pages:
Sets are created through the page list. After you create a Set, it will appear in the "Filter by" menu as an option for filtering the Index.
Tags allow for more complex collections of content. You can assign tags by right-clicking a page in the page list and choosing “Settings”. A page can have any number of tags and multiple tags can be collected into one Index.
If nothing matches the Thumbnail Index’s filter, it will display three square placeholders while you are editing, to indicate the presence of a Thumbnail Index.
Thumbnail Appearance
To choose which image represents the page inside the thumbnail index, right-click a page in the Pages menu and open Settings. Use the “Thumbnail” menu to select or upload an image or video to represent that page in your Thumbnail Indexes. To hide a page from all Thumbnail Indexes while keeping it accessible, uncheck the checkbox next to the Thumbnail Menu.
In the settings menu for each Thumbnail Index, you can also choose to render the Title and the Tags inside the caption area of the gallery. Style them inside your CSS through .caption .page-title and .caption .tags / .caption .tags a.