Looking for logging into the Joomla Form Custom Validation site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Joomla Form Custom Validation site. After that you can login as usual with your login credentials.
https://docs.joomla.org/Client-side_form_validation
https://docs.joomla.org/Form_validation
https://docs.joomla.org/Server-side_form_validation
https://techjoomla.com/developers-blogs/joomla-development/some-useful-custom-validators-for-client-side-form-validation-in-joomla.html
https://joomla.stackexchange.com/questions/4043/how-can-i-provide-a-custom-message-for-a-failed-jformrule-validation