Could you check that the problem is not the pattern. ie its trying to check if the empty value matches the regex in the pattern

the pattern works in J3 (saving with empty value gives no error) and gives this behavior in J4, so the issue is not in the pattern, but in the handling of the pattern

I am surprised it works in j3 because the pattern is a validation rule and an empty field doesnt match the pattern

anyway if you use type=email then the browser does it for you

anyway if you use type=email then the browser does it for you

sure, but this is an example of what seems like a B/C. There are patterns developers use that are not in the type list :)

unless I am very much mistaken html5 pattern validation is done by the browser not joomla

You are mistaken (sorry), issue is in validate.js
it validates against the pattern only when length of the field is not 0
if length is zero it checks if it is required (which it isn't)
then it should return true, but it return false (where the validation in J3 correctly returns a true)

because it returns a false, the error is thrown.

So somebody with knowledge of JS should have a look at line 685 of file ./media/system/js/fields/validate.js

pattern=".*@.*\..*"

Is this only a test or are you using something with this regex in real life? It would not be valid, as phil@myInternalServer is a valid email address and would fail that pattern.

pattern=".*@.*\..*"

Is this only a test or are you using something with this regex in real life? It would not be valid, as phil@myInternalServer is a valid email address and would fail that pattern.

this is just a simple test to show the B/C issue with J4 form field validation :) #noworries

Closing as there is PR #34124.