Question

Zend Form Validation: Is there a validator that is the opposite of Identical (i.e., notIdentical)?
How would I check that an input is not identical to ‘str’?

Answer 1

AFAIK there is not something like NotIdentical. Have you tried your own validator in that way?:

class My_Validate_NotIdentical extends Zend_Validate_Identical
{
    public function isValid($value)
    {
        return !parent::isValid($value);
    }
}

It just simplest solution – you should also change validation messages etc.