Custom Fields
The Interface
Validation tab
Form Tools 2.1.4 added the option to offer field validation in your Form Tools forms. We implemented this as a field-type specific feature, since certain validation rules only make sense for certain field types. For example, you won't need a "valid email only" validation rule for a group of checkboxes or a WYSIWYG field, but you would for a textbox.
The Validation tab lets you create and customize those validation rules.