Sing App uses really great validation plugin -
parsley.js. It's better to
let it say itself:
Javascript forms validation.
Powerful, UX aware & Dead simple.
Never write a single javascript line anymore to validate your forms FrontEnd. Parsley will do that for you – and do it right –, thanks to its powerful DOM-API !
To activate it you need to add data-validate="parsley" to your form to make it work. That's it.
If you want to add step-by-step validation with wizard please check
this guide.