registration form validation on blur

I would like to change the validation behavior from "onChange" or "focus" to "blur" so that the red validation message does not already appear during typing. It is really discouraging the user when he did not even finish typing his email and the form already shouts at him to not make mistakes.

Not without modifying core files, which we do not support. Form validation jQuery is prepared in the below file where you'd need to send custom jQuery Validate options to turn off keyup validation.

libraries/CBLib/CB/Legacy/cbValidator.php

Validate on blur is as useful as validate on submit. Meaning the user tends to just ignore it. Validate on type is typehinting which is more helpful than telling you later that you screwed up after you've moved past the input. It's a 50/50 split UX wise which is best and comes down to personal opinion at that point I suppose.

We've taken steps to make the errors non-intrusive (no bright backgrounds around the error), but you could use CSS to further make the errors less intrusive if you wanted. A lot of it also comes down to what the field is asking of the user. A better approach is to probably delay the type validation by a few seconds instead of immediate feedback