Syntax highlighting via Prism.
Place a <prism-highlighter> in your document, preferably as a direct child of
<body>. It will listen for syntax-highlight events on its parent element,
and annotate the code being provided via that event.
The syntax-highlight event's detail is expected to have a code property
containing the source to highlight. The event detail can optionally contain a
lang property, containing a string like "html", "js", etc.
This flow is supported by <marked-element>.