Features
Small tutorials aim to teach you all the features of Validatious step by step. Feature tutorials typically build upon each other, so if you see something you don't understand, try a previous tutorial and chances are you'll find an explanation.
HTML extension
With the HTML extension you can add validation, custom error messages and more simply through semantic HTML. This will probably serve most, if not all, of your form validating needs.
Reporting extension
The Reporting extension contains the implementation of Validatious' default error reporting. It gives you a customizable field centric reporting model. If you need to completely override the error reporting you can leave out this entire extension and save som kB's.
DSL extension
The DSL extension provides a powerful and expressive API for programatically validating forms. This can be useful in cases where you don't want to, or simply cannot use the HTML extension. Additionally, programatically adding validators allows for arbitrary compound validation rules.
Core API
The core API offers the full flexibility of Validatious, only with slightly more verbose code than with the DSL extension for adding validations. You will probably use the core API first and foremost to configure the behaviour of Validatious and add custom validators.