(I’ll go over more about YAML syntax in a later section.) You then create your HTML structure in another file, such as sidebar.html. You store your data items in a YAML file using YAML syntax. Here’s the basic approach in creating a table of contents. Not many Jekyll themes actually have a robust table of contents, which is critical when you are creating any kind of documentation or reference material that has a lot of pages. This setup is most common when you’re trying to create a table of contents. One of the most interesting features of Jekyll is the ability to separate out data elements from formatting elements using a combination of YAML and Liquid.