Good catch, especially as I missed the underscore, rendering the code buggy. (Rule of thumb: never code after 24h).

Actually, while the language tag is turned into a css class, it is unclear how the tag is formed, especially in hoedown. The only one coming close to documenting something understandable is pandoc, that also allows its own tagging syntax. http://johnmacfarlane.net/pandoc/README.html#fenced-code-blocks

Specifications, who needs them? :/