template_renderer.rb

module ActionView   
    class TemplateRenderer < AbstractRenderer #:nodoc:
      # Determine the template to be rendered using the given options.
        def determine_template(options)
          keys = options.has_key?(:locals) ? options[:locals].keys : []
          if options.key?(:body)
            ...
          elsif options.key?(:file)
            with_fallbacks { find_file(options[:file], nil, false, keys, @details) }
          ...
        end
    end