- the problem : how to serve different view templates to their hybrid mobile apps and desktop clients at the same time?
 - the solution: introduce a new feature to Rails. One that will enable single action to serve different templates.
 
- conceptually: "variant" is a symbol whose name constitutes a part of the variant naming scheme
 - naming scheme is: action_name.html+variant_name.erb -> new.html+mobile.erb
 - technically: a symbol, or an array of symbols, that get assigned with a call to request.variant=
 - use request.user_agent to test the client type
 - if no "variant template" is found, the default action template gets rendered
 - it works for partials just the same
 
browser gem
- it exposes browser object to the ActionController
 - transparent API:
 
- browser.chrome?
 - browser.bot.search_engine?
 - browser.device.mobile?
 - browser.platform.linux?