Shall, Should, May 2 : 'Shall' indicates that a requirement is mandatory. 'Should' indicates an advisory statement. 'May' implies the right to use discretion
Ministry of Business, Innovation and Employment, Glossary of terms and acronyms, Wellington, New Zealand 2010. http://wwwsosh.govt.nz/resources/glossary-u.shtml, (Occupn Hlth and Sfty - Brit) {530}