Per What is syntax highlighting and how does it work?, it would appear that adding

<!-- language: lang-el --> 

prior to code blocks in Emacs should enable syntax highlighting. Unfortunately it does not yet appear to be enabled, or is missing something. As example, I added the above to the answer in http://emacs.stackexchange.com/a/81/104, and it is not highlighted. Is there a specific tag that is also required, and could we just presume that Elisp should be the default highlighting for the emacs community?