When you submit the form, the value is presented with debug_dump(), so strings are quoted and array values listed.

: - Stop the submitted form from bring processed
: - Don't process the form, redirect to another page (e.g. login after session timeout), and remember the values for when they return.

or back to examples 

<?php
	$field = new form_field_email($form, 'Email');
	// $field->domain_check_set(false);
	// $field->domain_error_set('Your email does not appear to be for a valid domain.', 'Tick if you are sure this is valid.');
	$field->format_error_set('Your email does not appear to be correct.');
	$field->min_length_set('Your email is required.');
	$field->max_length_set('Your email cannot be longer than XXX characters.', 200);
?>