Example form is linked to a database table, but won't be saved in this example.
When you submit the form, the value is presented with debug_dump(), so strings are quoted and array values listed.
<?php $field = new form_field_postcode($form, 'Postcode'); $field->db_field_set('postcode'); $field->format_error_set('Your postcode does not appear to be correct.'); $field->required_error_set('Your postcode is required.'); ?>