Simple text field with minimum characters.

Hi everybody,

Im looking for a solution for my problem:

I want a simple text field in de contact entity, with a minimum AND Maximum characters lenght of 5.

now it is possible to specify a maximum. but not to indicate a minimum. The format of the form must be (days / months). So from 01-01 to 31-12. Preferably with the first two values ​​that can go up to 31 and the last two values ​​to 12. But just a minimum would solve a large part of the problem.

I understood that this might be possible through javascript in the onchange event?

If this is not recommended because it is too much work, then I would also like to hear that.

Regards,
Daimy Tamis