Where can I use HAML in Octopress?

So, according to the Octopress official page, it has HAML integration plugin. Naturally, I gave it a try. I backed up my source/_includes/custom/head.html file, converted it to haml and saved it as source/_includes/custom/head.haml. It gave me an error.

I tried doing the same with source/_layouts/page.html file, and it worked like a charm.

My question is, where can I and where can I not use HAML in an Octopress blog?

AS you can see from the source code, the HAML is only processing pages content.

See the convert && output_ext methods.

https://github.com/imathis/octopress/blob/master/plugins/haml.rb

module Jekyll
  require 'haml'
  class HamlConverter < Converter
    safe true
    priority :low

    def matches(ext)
      ext =~ /haml/i
    end

    def output_ext(ext)
      ".html"
    end

    def convert(content)
      begin
        engine = Haml::Engine.new(content)
        engine.render
      rescue StandardError => e
          puts "!!! HAML Error: " + e.message
      end
    end
  end
end