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
$field = new form_field_password($form, 'Password');
$field->db_field_set('password');
$field->min_length_set('Your password is required.');
$field->max_length_set('Your password cannot be longer than XXX characters.');
$field->info_set('- obviously do not save to the database like this.');
?>