Simply, the specification for custom data attributes states that any attribute that starts with "data-" will be treated as a storage area for private data (private in the sense that the end user can't see it - it doesn't affect layout or presentation).
This allows you to write valid HTML markup (passing an HTML 5 validator) while, simultaneously, embedding data within your page
CodePress is web-based source code editor with syntax highlighting written in JavaScript that colors text in real time while it's being typed in the browser.
This is a REAL odometer style javascript counter, where you can actually see the numbers spining. No Flash, it's all css and javascript. It can serve multiple purposes, like a live visit counter or a cashier style counter on a shopping website. Well, anything that involves updating a numeric value dynamically. It can also be used a fixed counter, like the one you can generate with a server script, but of course that isn't nearly as much fun as updating it in real time.