Stepper documentation is lacking content

I'm missing some points in the steppers documentation - especially at the feedback/validation sections. Feedback step: "If you want, for example, to check if an e-mail exists in your DB, you can define a feedback function with data-feedback attribute in your next button. " ... and if so I don't want the user to continue to the next page but make him choose another email. The documentation only shows the nextStep() function which would be the successfully option. What do I do when I want to prevent to user to continue? Validation Step: The documentation's example doesn't use the data-validator tag at all (and the loading circle loads inifinitely). I unsuccessfully tried to use the validate stepper. I added the data-validator tag to the button, added a simple, false returning function to the js and I still could continue. What's the difference between validator and feedback? They both seem to be some kind of validation.

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