It would be nice if we could display custom validation errors for:

• Selecting (or not selecting) a certain number of boxes on checkbox fields (e.g. minimum of 2 boxes must be checked, or maximum of 4 boxes can be checked)
• Making sure the values of two fields are equal. For example, when electronically signing a form using a single line field, the value the user enters must equal the value of the "First Name" and "Last Name" fields earlier in the form combined with a space.
• Date fields that are greater/less than specific date values. For example if the user picks 2/8/2004 as their birth date, we want to display a validation message underneath the field that says they must be 18 years or older. Or for From/To fields, we want to make sure the date picked on the From field is less than the date picked on the To field (e.g. on job applications).

Right now we use JavaScript to manually display messages but this inevitably makes our forms very complex and hard to maintain/upgrade.