How do I display a dedicated error message, if string fails to validate

Drew McLellan said:

Instead of for="all" use for="fieldID" to show errors for a specific field.

I tried

<perch:error for="regcode" type="format">

and

<perch:error for="regcode" type="general">

and both do not appear when an incorrect string is entered. The form just doesn't get sent.
Validation works, though, as when I enter the correct string the form sends perfectly.

The input field looks like this:

<perch:input type="text" required="true" id="regcode" label="Registrierungscode" helper="Summit::check_code" />

The helper function looks like this:

class Summit extends PerchAPI_Factory
{
    public static function check_code($regcode) {
        if ($regcode==="somecode") {
            return true;
        }

        return false;
    }
}

Worked like a charm.
Thank you, Drew.