Signup form validation question

Hey, thanks for this great framework,.. I have a question:

How come in the INVO demo app the register.volt template this simple code:

                <p class="help-block">(required)</p>
                <div class="alert" id="name_alert">
                    <strong>Warning!</strong> Please enter your full name
                </div>

actually checks for the user input and if the input is missing or is invalid shows the warning... I couldn't find any function that creates the validation behaviour.. I am trying to do the same using the default php template engine.(.phtml) but with no succcess, i get the warning displayed directly.. is it a feature of volt or should i dig deeper in the invo code?

Thank you very much champs!