From humble beginnings, forms in HTML5 are now tremendously flexible and powerful, providing natively much of the functionality that we as developers have been adding in with JavaScript over the years. The new input types alone are a welcome addition, especially for those of us who use dynamic soft keyboards, and the new attributes offer fine control over form elements.
But the native validation puts the icing on the cake, replacing the many different JS libraries that have been written to solve the client-side validation problem. And while that’s welcome, the Constraint Validation API really gives full power to developers, enabling custom validation across different browsers and platforms in a fully standardized way.
With the extra styling capability provided by new CSS pseudo-classes, HTML5 forms are a prime example of the power of the new web platform.