I am a Ruby on Rails developer, working on this technology from past 7 months. while working on Rails many times i encountered `yaml` files. 

As i encountered `yaml(yet another mark-up language)` is used to store the static content that needed to load before the server starts( like in `I18n` language translation ) and some are used as a switch to store `'boolean'` values.

Recently in some of SO questions i saw `haml` used in rails, As far as i know both are mark-up languages. What is the difference between these two and what to prefer and not-to while using rails.

Please shed some light on this :)