Expandable Tree pattern does nothing in Plone 5.2.1

After successfully installing Patternslib in my Plone site and testing other patterns with success, pasting the following test code for the Expandable Tree pattern into a page through TinyMCE's "View Source" tool (with HTML filtering disabled completely):

<ul class="pat-expandable">
  <li class="folder">Folder name</li>
  <li class="folder open">Folder name
    <ul>
      <li class="document"><a href="#">Document name</a></li>
      <li class="folder closed">Folder name
        <ul>
          <li class="document"><a href="#">Document name</a></li>
        </ul>
      </li>
      <li class="document"><a href="#">Document name</a> </li>
      <li class="document"><a href="#">Document name</a> </li>
      <li class="document"><a href="#">Document name</a> </li>
      <li class="document"><a href="#">Document name</a> </li>
      <li class="document"><a href="#">Document name</a> </li>
    </ul>
  </li>
  <li class="folder">Folder name</li>
  <li class="folder">Folder name</li>
  <li class="folder">Folder name</li>
</ul>

...produces an ordinary bulleted list (with no special behaviour at all).

My plone site versioning is as follows:

Plone 5.2.1 (5208)
CMF 2.4.2
Zope 4.1.3
Python 3.6.9 (default, Jan 24 2020, 11:58:01) [GCC 4.8.5 20150623 (Red Hat 4.8.5-39)]
PIL 6.2.1 (Pillow)
WSGI: On
Server: waitress 1.4.3

...and the plone.patternslib version pulled and included was 1.1.0.

The issue names no source file or test. First reproduce the Expandable Tree markup in Plone 5.2.1 with plone.patternslib 1.1.0, then trace the Plone integration for the Expandable Tree pattern. Done means the supplied list receives the expected expandable and collapsible behavior instead of remaining an ordinary bulleted list.