Currently there's very little ability to do Custom Field validation, just the very basics, and those aren't very granular (for example, the max length of a field is only available in increments of 10 and you can only limit the field of a text field the max length).
I'd like to see much more input validation, which would eliminate a lot of back-and-forth with careless users entering invalid data.
For example, the ability to:
- require a user to enter exactly 10 characters, no more, no less
- restrict numbers to ranges
- restrict text fields to certain characters or prohibit certain characters
- restrict dates, times and timestamps to ranges or greater-than/less-than a certain date or date calculation
- etc, i.e. typical input validation stuff
