CRM_Core_PseudoConstant::register('CRM_Contact_BAO_Contact', 'contact_type'); CRM_Core_PseudoConstant::register('CRM_Contact_BAO_Contact', array( 'contact_sub_type' => array( 'Volunteer' => ts('Volunteer'), 'Donor' => ts('Donor'), 'Client' => ts('Client'), ), ));This API allows other parts of the application to use these constant values consistently throughout the codebase, without relying on hard-coded values. In the example above, the package library is "CRM_Contact" which is a part of CiviCRM.