The Form Validator component models.
The form field, identified by unique key, which stores a value, validators of that value, and validation errors (if any).
A list of validators for a field.
A field validator which evaluates to an error string (invalid) or nothing at all (valid).
A list of field values to be validated.
A field value to be validated.
The corresponding error messages of an invalid field value(s).
The corresponding error message of an invalid field value.
The form model which stores a list of fields for input and validation.