# Navigation and tables of contents

We create website navigation and tables of contents for books in the _data/meta.yml file of the Electric Book template. The data in the meta.yml file is written in a syntax called yaml, which is very strict (e.g. a slight error in indentation can prevent your whole book from building), but once you get the hang of it, adding your book’s information for output will be easy enough.

You can test whether your yaml is valid by pasting it into the box on yamllint.com and clicking ‘Go’. The yamllint validator will tell you whether it is valid or not, and will tell you on which lines errors appear with relative accuracy.

The _data/meta.yml file includes all of the metadata of your book, from the series name and ISBN to the names of each file for your contents page. By default, the title page, copyright page and contents page pull information from the _data/meta.yml file.

## How to edit the nav and TOC

1. In the works: section, and then in the directory section for your particular book, and then under products:, scroll down to the output format you want to edit. E.g. web:.
2. Edit (or create, if it doesn’t exist) a toc: section indented by two spaces below, say, web:.
3. For each navigation or table of contents entry, add a line for each of file: "", label: "" and, optionally, id: "" and class: "", for each TOC entry. The first line in the TOC entry should have a -, like a bullet point.
4. To nest entries beneath an entry, give the parent entry a children: line, then indented on the next line add file: "", label: "", and so on.

The label can be anything you want, but is usually the heading of the section you are including in the table of contents, since the label is what displays in the table of contents or navigation.

The file is the filename of the file that the item will link to, without a file extension.

The optional id is usually the slug of the heading (the heading stripped of spaces, punctuation, and uppercase letters).

Here is an example:

        nav:
- label: "Chapter Two"
file: "02"
id: "2-goodbye-world"
children:
- label: "subsection"
file: "02"
id: "example-id"


If you only add a toc for print or web output, the template will try to read that TOC for the other formats, too, so that you don’t have to repeat your toc for every format. If you want a different TOC for a given format, you can give that format it’s own toc section.

Note that the toc and nav sections in meta.yml are structurally identical. In many projects they are the same except that one starts with toc and the other nav. A PDF will never need a nav, but a website output might have both a toc (which displays a Table of Contents on a body text page) and a nav (which defines the dropdown menu on a website).

## Using IDs for accurate linking

For PDFs, ids ensure that the TOC contains accurate page numbers in books where chapters start with a blank left-hand page.

Note that within a file, an id can only be used once, as ids are unique. So, for example, if you have two subsections in one file both titled ‘Extra Information’, the ids will likely be extra-information and extra-information-1.

If you are having trouble finding the slug for the id: generate a web version of your book, go to the heading, right click on it and choose ‘Inspect’ (you may need Cmd Shift C on Mac to get element-specific information). In the Elements box you should see a line of code that gives you the element’s id. For a level-1 heading called ‘Chapter 5: Animals’, the id is shown in this line of code followed by the label:

<h1 id="chapter-5-animals">Chapter 5: Animals</h1>


Here chapter-5-animals is the id.

Note that to see files in website navigation at all, they must be included in your web output in the nav: section of _data/meta.yml. Otherwise you have to know the URL of the page you’re looking for and enter it directly into the browser’s address bar.

## Adding classes to control design

You can optionally add a class line to specify the class of an element. For example, frontmatter in the book (such as a preface, whose entry in the TOC which you might want to look different from chapter content) can be given a different style by adding the line class: "frontmatter-reference" to the node of the metadata where you defined its label, file and id.

By default, frontmatter-reference in PDF output can provide a lower-roman-numeral page number, if lower-roman has been set in the \$frontmatter-reference-style variable in your book’s print-pdf.scss and/or screen-pdf.scss stylesheets.

## Generating the TOC

Once you have constructed your metadata for all of the outputs of the book that you’re outputting (for example, print PDF and web formats), use:

{% include toc %}


in a markdown file. This tag generates a table of contents. In the default template you can see this in the 0-3-contents.md file.

## Epub TOCs

Epubs have special TOC needs. See the epub output section on metadata.

## TOCs outside of books

Sometimes you may want to place the TOC of a book on a page that isn’t inside that book’s directly – on the home page, for instance. To do this, you need to tell the toc include which book’s TOC you’re generating, like this:

{% include toc book="moon-potatoes" %}


By default, the toc include will generate the TOC of the book in the book folder.

## TOCs of book parts

Sometimes you may want to output a TOC of only part of a book. For instance, say your book has four parts, each containing several chapters. You may want each part page to include a TOC of its chapters.

In _data/meta.yml, the chapters you want are listed within each part’s children node.

To list only those in TOC, you need to tell the toc include to start there, with the part’s children.

To do this, you add a start parameter to the include tag, pointing to that children node.

It can take some advanced technical know-how to write the ‘address’ of that node of data. Here is an example.

We need to add the following two lines to our part page’s markdown file. The first assigns the children node’s data to a variable. The second includes the TOC on the page, using that variable:

{% assign my-chapter-list = site.data.meta.works[0].products[site.output].toc[4].children %}

{% include toc start=my-chapter-list %}


If you want to know how that works, let’s break it down. In

site.data.meta.works[0].products[site.output].toc[4].children


each dot or [ means we’re drilling down into the data by one level:

• site.data.meta refers to all the data in _data/meta.yml.
• .works refers to the works node in that file.
• [0] refers to the first work in the works node – that is, the first book in your project. If you wanted the second book in your project, you’d use [1]. The numbering of nodes in data starts at 0.
• .products refers to the products – or output formats – of the work.
• [site.output] refers to the current site output format, which will be one of the child nodes of products.
• .toc refers to that output format’s toc node.
• [4] refers to the fifth item in the toc node, which in our example is the part for which we want to list the chapters.
• .children refers to the list of chapters inside that toc[4] part. That’s what we want for our TOC!

Finally, in start=my-chapter-list we’re telling the TOC include to start listing chapters at my-chapter-list, which we just defined.

Websites and apps can also include pages that are not part of a book, like ‘About us’ and ‘Contact us’. These are created as markdown files in the project’s root directory.

They are added to the nav by listing them in _data/nav.yml. That file is organised by language, since your project may include different languages.

If you only include nav items for your project language (e.g. en for English), then all translated pages will include the English items, too.

If you include translations in your nav.yml, you must include the relevant files that you point to in that language’s folder in the project root. For example, if you have this entry in your nav.yml:

fr:
- label: "À propos de nous"

then you must have a fr/about.md file in your project, or the link in your navigation will not work.