I'd like to override the registration form (I am not using bootstrap on the front-end), but I cannot see where I can change the behaviour of the registration form. I'd like to implement my own tab navigation for a form, but I cannot see how this is done.
As far as I understand the com_users /registration view is being changed by a plugin, but how can I override this?

Sorry if it is a bit vague, but I can't get my head around this,
Thanks for any help
Bernhard