[EvanPlaice]

We have a lightweight extensible markup language. It's called XML.

When HTML web components are fully supported in all browsers, it'll be possible to create custom markup elements to extend HTML to include custom DSLs (Domain Specific Languages).

I already have a library (ng2-markdown) that provides a template tag that can parse markdown (incl syntax highlighting) in the same manner that the script tag can parse javascript.

If a parser is already available in javascript, it's not exceedingly difficult to create new HTML elements.