| Module | ActionView::Helpers::AtomFeedHelper | 
| In: | lib/action_view/helpers/atom_feed_helper.rb | 
Full usage example:
  config/routes.rb:
    ActionController::Routing::Routes.draw do |map|
      map.resources :posts
      map.root :controller => "posts"
    end
  app/controllers/posts_controller.rb:
    class PostsController < ApplicationController::Base
      # GET /posts.html
      # GET /posts.atom
      def index
        @posts = Post.find(:all)
        respond_to do |format|
          format.html
          format.atom
        end
      end
    end
  app/views/posts/index.atom.builder:
    atom_feed do |feed|
      feed.title("My great blog!")
      feed.updated(@posts.first.created_at)
      for post in @posts
        feed.entry(post) do |entry|
          entry.title(post.title)
          entry.content(post.body, :type => 'html')
          entry.author do |author|
            author.name("DHH")
          end
        end
      end
    end
The options for atom_feed are:
Other namespaces can be added to the root element:
  app/views/posts/index.atom.builder:
    atom_feed({'xmlns:app' => 'http://www.w3.org/2007/app',
        'xmlns:openSearch' => 'http://a9.com/-/spec/opensearch/1.1/'}) do |feed|
      feed.title("My great blog!")
      feed.updated((@posts.first.created_at))
      feed.tag!(openSearch:totalResults, 10)
      for post in @posts
        feed.entry(post) do |entry|
          entry.title(post.title)
          entry.content(post.body, :type => 'html')
          entry.tag!('app:edited', Time.now)
          entry.author do |author|
            author.name("DHH")
          end
        end
      end
    end
The Atom spec defines five elements (content rights title subtitle summary) which may directly contain xhtml content if :type => ‘xhtml’ is specified as an attribute. If so, this helper will take care of the enclosing div and xhtml namespace declaration. Example usage:
   entry.summary :type => 'xhtml' do |xhtml|
     xhtml.p pluralize(order.line_items.count, "line item")
     xhtml.p "Shipped to #{order.address}"
     xhtml.p "Paid by #{order.pay_type}"
   end
atom_feed yields an AtomFeedBuilder instance. Nested elements yield an AtomBuilder instance.