# File lib/action_controller/request.rb, line 154
    def format
      @format ||=
        if parameters[:format]
          Mime::Type.lookup_by_extension(parameters[:format])
        elsif ActionController::Base.use_accept_header
          accepts.first
        elsif xhr?
          Mime::Type.lookup_by_extension("js")
        else
          Mime::Type.lookup_by_extension("html")
        end
    end