Plugin fails to parse ++> into <details> with open state

[RenegadeScooter]

I am learning to use Eleventy and this looked like a useful plugin for its markdown-it parser so I added it to my project.
Line from my package.json: "markdown-it-collapsible": "^2.0.2",

---

Copied this code from the README

++> Click me!
Hidden text
++>

and pasted it into my Markdown document, only for it to fail to parse as shown

<p>++&gt; Click me!
Hidden text
++&gt;</p>

---

However, changing the > to + like this

+++ Click me!
Hidden text
+++

resulted in a <details> element without an open default state as normal

<details>
<summary><span class="details-marker"></span>Click me!</summary><p>Hidden text</p>
</details>

What's going on here?