ruby script/plugin install http://svn.codahale.com/xhtml_content_type/

xhtml_content_type is super easy to use. Add the method +sends_xhtml_with_correct_content_type+ to a specific controller, or to ApplicationController to make all controllers send XHTML properly:

  class ApplicationController < ActionController::Base
    sends_xhtml_with_correct_content_type
  end

+sends_xhtml_with_correct_content_type+ also accepts standard filter-style conditions, if you need them:

  class MySpecialController < ApplicationController
    sends_xhtml_with_correct_content_type :except => [:seriously_weird_action]
  end

  class MyOtherSpecialController < ApplicationController
    sends_xhtml_with_correct_content_type :only => [:the_only_regular_action]
  end

You can also explicitly specify an XHTML content type using this plugin:

  def xhtml_only_action
    render :content_type => :xhtml
  end

If you're declaring the content type in a element as well, you should do something like this:

  < meta http-equiv="content-type" content="<%= controller.preferred_content_type %>; charset=UTF-8" />

There is currently no advanced documentation for this plugin.