Enums or enumerations or enumerator types are those little data structures that can be used to define a set of named values. More like constants. For instance, a contract status which can be “permanent”, “temp”, or “apprentice”. Or a order status that can be “ordered”, “dispatched”, “shipped” etc.| Amit Merchant
PHP RFC: Never Parameters (v2)| wiki.php.net
The PHP Foundation — Supporting, Advancing, and Developing the PHP Language| thephp.foundation