How To Validate a Custom Field For Minimum Value?

Hi,

I have a custom field for the add listing form that requires a minimal value, unfortunately the custom field settings only offers validation for a required field, is there a way to check a text field for min or max numeric values?

Any input is much appreciated.

P.S. Suggestion for next update, besides more extensive form validation options, also add a drag and drop function to determine the order of the custom fields on the form.