In browsers that do support HTML5, h5Validate adds some much-needed features, such as the ability to customize the user interface when an input fails validation.
For demo and usage, see the h5Validate homepage.
A lot has changed since I wrote this library in 2010. So much, in fact, that I've started a new project based on the great work we did here. It's called h5v2. It's brand new, we haven't even ported the unit tests, yet.
Wouldn't you like a library like h5Validate written to work with node-style modules, Browserify, and web components? I'd love your help. Take a look at the issues and contribute!