bookdown Authoring Books and Technical Documents with R Markdown

We have explained how cross-references work for equations (Subsection 2.2.1), theorems (Subsection 2.2.2), figures (Section 2.4), and tables (Section 2.5). You can also reference sections using the same syntax \@ref(label), where label is the section ID. By default, Pandoc will generate an ID for all section headers, e.g., a section # Hello World will have an ID hello-world. We recommend you to manually assign an ID to a section header to make sure you do not forget to update the reference label after you change the section header. To assign an ID to a section header, simply add {#id} to the end of the section header. Further attributes of section headers can be set using standard Pandoc syntax.

When a referenced label cannot be found, you will see two question marks like ??, as well as a warning message in the R console when rendering the book.

You can also create text-based links using explicit or automatic section IDs or even the actual section header text.

The Pandoc documentation provides more details on automatic section IDs and implicit header references.

Cross-references still work even when we refer to an item that is not on the current page of the PDF or HTML output. For example, see (2.2.1) and Figure 2.4.4.