You don't know where "doc" is coming from from a snippet like that. I use logic moderately similar to that for my blog software. If I'm writing the blog post, pretty much pass through what I wrote. If it's a comment (back when I had them), process the heck out of it. The blog post itself is a blob of HTML, basically.

I do not currently write my blog posts in a templating language (any more than anyone else does), though Hamlet [1] has me sort of tempted as it is so close to what I write anyhow.

[1]: http://www.yesodweb.com/book/templates