@Moondeer Yeah, I stumbled upon your plug-in; it's awesome and way more polished than my approach. Mine is mostly a proof of concept. Nevertheless, I thought it worthwhile to experiment with monkey patching the built-in highlight shortcode for two reasons.

First, it works without JavaScript, and second, Hugo template code "just works." So no jumping through hoops is necessary.

But, with @manton rolling out changes today, my plug-in will probably soon be obsolete.