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Details is an extension that creates collapsible elements that hide their content. It uses the HTML5 <details><summary> tags to accomplish this. It supports nesting and you can also force the default state to be open. And if you want to style some different than others, you can optionally feed in a custom class.

The Details extension can be included in Python Markdown by using the following:

import markdown
md = markdown.Markdown(extensions=['pymdownx.details'])


Details must contain a blank line before they start. Use ??? to start a details block or ???+ if you want to start a details block whose default state is 'open'. Follow the start of the block with an optional class or classes (separated with spaces) and the summary contained in quotes. Content is placed below the header and must be indented.

??? optional-class "Summary"
    Here's some content.

??? multiple optional-class "Summary"
    Here's some content.

Example Details

Open styled details
Nested details!

And more content again.

???+ note "Open styled details"

    ??? danger "Nested details!"
        And more content again.

It is also possible to provide only a class. If this is done, the title will be derived from the first class.

Example Class from Title





??? success

??? warning classes

Details will be output in the format below. The content will always be encapsulated in tags of some kind.

<details class="optional-class"><summary>Text</summary><p>Content</p></details>

Browser Support

Unfortunately, due to how new <details><summary> tags are, not all browsers support them yet. In order to have them supported in all new browsers, you will have to provide some fallback styling and JavaScript until all browsers catch up.

This extension's goal is not to provide you with the perfect polyfill, but this is a basic example that provides basic support. There are more elaborate polyfills available that support jQuery, add keyboard events, or even support back to IE8. Feel free to modify what is here or find a solution that fits your needs.

Basic Polyfill Setup

Here is the basic CSS that that can be used. It is meant to provide a consistent CSS in both browsers that support <details><summary> tags and those that do not.

details {
  display: block;

details[open] > summary::before {
  content: "\25BC";

details summary {
  display: block;
  cursor: pointer;

details summary:focus {
  outline: none;

details summary::before {
  content: "\25B6";
  padding-right: 0.5em;

details summary::-webkit-details-marker {
  display: none;

/* Attach the "no-details" class to details tags
   in browsers that do not support them to get
   open/show functionality. */[open]) > * {
  display: none;
}[open]) summary {
  display: block;

And below is the JavaScript that will detect browsers that do not support <details><summary> tags and apply a no-details class to all details in those browsers. It will also attach a click event that will toggle the open state. The CSS above will target the no-details class and the open attribute to hide/show the content of your <details> tag. Just run the code after the HTML content is loaded.

There are plenty of things that aren't covered here, like jumping to a footnote or ID inside a closed polyfilled detail element, but this is left up to the user to figure out, or for a complete 3rd party polyfill.

(function () {
'use strict';
 * Converts details/summary tags into working elements in browsers that don't yet support them.
 * @return {void}
var details = (function () {

  var isDetailsSupported = function () {
    // Detect if details is supported in the browser
    var el = document.createElement("details");
    var fake = false;

    if (!("open" in el)) {
      return false;

    var root = document.body || function () {
      var de = document.documentElement;
      fake = true;
      return de.insertBefore(document.createElement("body"), de.firstElementChild || de.firstChild);

    el.innerHTML = "<summary>a</summary>b"; = "block";
    var diff = el.offsetHeight; = true;
    diff = diff !== el.offsetHeight;

    if (fake) {

    return diff;

  if (!isDetailsSupported) {
    var blocks = document.querySelectorAll("details>summary");
    for (var i = 0; i < blocks.length; i++) {
      var summary = blocks[i];
      var details = summary.parentNode;

      // Apply "no-details" to for unsupported details tags
      if (!details.className.match(new RegExp("(\\s|^)no-details(\\s|$)"))) {
        details.className += " no-details";

      summary.addEventListener("click", function (e) {
        var node =;
        if (node.hasAttribute("open")) {
        } else {
          node.setAttribute("open", "open");

(function () {
  var onReady = function onReady(fn) {
    if (document.addEventListener) {
      document.addEventListener("DOMContentLoaded", fn);
    } else {
      document.attachEvent("onreadystatechange", function () {
        if (document.readyState === "interactive") {

  onReady(function () {


Last update: April 29, 2021