How not to make a custom renderer in Rails.
While wrangling with the issues the lead to the Excelinator gem, I wondered what it would take to not require any additional code in your Rails app to support Excel versions of existing CSV and HTML views. I learned a lot about how some of the Rails rendering pipeline works, and while it was waaay too much monkey-patching to actually use, it couldn't be forgotten. So I've turned this into a short talk - and here's the code.