Light Blue 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.
Files:
lib/parsley/parsley.js