Number Validation Rule for Digits Count

Ability to set the min and max rules for the number of digits in a number field, so "You should enter 8 digits" just like you can with a text field (Which I notice is incorrect, if you enter 8 in the rules then enter 8 in the UI it fails, if you enter 7 in the rules and 8 in the UI it works, I will report via a ticket).