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. It has been several years since I used the library myself. I leave it here because other people might find it useful. There are some open issues, and I have no intention of updating or maintaining this library myself. Pull requests are welcome.
If you'd like to become the new maintainer of this project, open an issue and we'll discuss it.