code: func serveFile(w http.ResponseWriter, r *http.Request, absPath string) {
  	if !strings.HasSuffix(absPath, ".html") && !strings.HasSuffix(absPath, ".md") {
  		http.ServeFile(w, r, absPath)
  		return
  	}
  
  	data, err := ioutil.ReadFile(absPath)
  	if err != nil {
  		serveError(w, r, absPath, err)
  		return
  	}
  
  	// AutoHeadingIDs is the only extension missing
  	data = blackfriday.Run(data, blackfriday.WithExtensions(blackfriday.CommonExtensions|blackfriday.AutoHeadingIDs))
  
  	title := ""
  	if m := h1TitlePattern.FindSubmatch(data); len(m) > 1 {
  		title = string(m[1])
  	}
  
  	servePage(w, r, pageParams{
  		title:   title,
  		content: data,
  	})
  }
docs: // serveFile serves a file from disk, converting any markdown to HTML.