How does the Reader function of Mobile Safari in iOS 5 work? How do I enable it on my site. How do I tell it what content on my page is an article to trigger this function?<
See Article Publishing Guidelines.
Here are APIs about how to read and parse: Readability Developer APIs. There's already a project you can refer: ruby-readability.
A brief history: The Safari Reader feature since Apple's Safari 5 browser embeded a codebase named Readability, and Readability started off as a simple, Javascript-based reading tool that turned any web page into a customizable reading view. It was released by Arc90 (as an Arc90 Lab experiment), a New York City-based design and technology shop, back in early 2009. It's also embeded in Amazon Kindle and popular iPad applications like Flipboard and Reeder.