Rack::XMLStylesheet is a rack middleware that makes changes on response body when the content type of responses is XML. It uses the rendered template path and checks on your public path (where the assets are placed) for a corresponding XSL file. If this XSL exists, then a processing instruction is added before the root element of the XML. This instruction helps the client of the response to transform the XML.
Suppose that you had requested the following resource:
GET /blogs/1/comments HTTP/1.1
Accept: application/xml
And the view rendered by your application is the following:
app/views/comments/show.tokamak
The response given by your application would be a XML like this:
HTTP/1.1 200 OK
Content-Type: application/xml; charset=utf-8
<?xml version="1.0" encoding="UTF-8"?>
<comments>
<comment>I liked this.</comment>
</comments>
The middleware uses the template path ('comments/show.tokamak') and try to find a corresponding XSL into public path, with the extension '.xsl'.
If it's there, then the response body is modified:
HTTP/1.1 200 OK
Content-Type: application/xml; charset=utf-8
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="/xsl/layouts/default/comments/show.xsl"?>
<comments>
<comment>I liked this.</comment>
</comments>
In your Gemfile:
gem 'rack-xml_stylesheet', :require => 'rack/xml_stylesheet'
In your environment.rb:
require 'rack/xml_stylesheet'
config.middleware.use "Rack::XMLStylesheet"
Have in mind that the middleware has only Rails 2.3.x support for now.