Add option to enforce maxlength server side.

Same here, using adminimal theme. The counter works, but there is no validation.

I have tried with a user with no bypass permission.

Maxlength 1.0.0-beta5
Core 8.8.3

Some more info:

This occurred on formatted text, CKEditor. One would expect a JS validation to stop the form submit when the counter is negative, but it does not. To mitigate the issue, the Force truncate and Safe truncate html options must be used.

On raw text, all is fine.

Using the patch in https://www.drupal.org/project/maxlength/issues/2916687 allows to set a Javascript "soft" limit, but we should add an option to defined if a server side validation should occur. The use case is if we want, for example, to add a maximum text length restriction on a existing field, whose content may already be greater than the limit. We can not use truncate text here as we would loose data without warning the editor.

I've updated the issue title and description for clarity. I've marked it as a feature request, though there's an argument to be made that it's a bug.

This feature request is no longer relevant per #2916687: Soft limit does not work on plain text fields because the Maxlength HTML attribute is used so marking closed, works as designed.