How to add dropdown menu on tab / tabset [rmarkdown / bootstrap]

Question

Documentation for Bootswatch suggests I can use a dropdown menu from a tab in a tabset:

How can I achieve this with Rmarkdown? I've tried:

# SECTION 1 {.tabset .tabset-fade}

## Section 1.1 

## Section 1.2 {????something here?????}
 ### Section 1.2.1  <<<<<<<<< want this to appear under the dropdown menu

Answer 1

This is now available within the development version of rmarkdown, which you can install this via devtools::install_github("rstudio/rmarkdown"). To add a dropdown menu, you must add .tabset-dropdown to the class header as follows:

---
output: html_document
---

# Heading {.tabset .tabset-dropdown}

## Dropdown 1

## Dropdown 2

## Dropdown 3 

## Dropdown 4