The validation code is here https://github.com/NodeBB/NodeBB/blob/master/public/src/client/register.js. You can write a plugin to validate your own inputs.

Benchpress had no built-in way to do this. You'll need to add a helper in order to do subtraction. https://community.nodebb.org/topic/11801/help-with-using-helpers-inside-my-theme

@pitaj sorry i cant resolve this topic

Awesome sometimes it's as simple as that. Thanks a lot.