Static Keyword
Class Abstraction
Classes and Objects (PHP 5)
PHP Manual

## Class Constants

It is possible to define constant values on a per-class basis remaining the same and unchangeable. Constants differ from normal variables in that you don't use the $ symbol to declare or use them.

The value must be a constant expression, not (for example) a variable, a class member, result of a mathematical operation or a function call.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

Example #1 Defining and using a constant

`<?php
class MyClass
{
const constant = 'constant value';
function showConstant() {
echo self::constant . "\n";
}
}
echo MyClass::constant . "\n";
$classname = "MyClass";
echo $classname::constant . "\n"; // As of PHP 5.3.0
$class = new MyClass();
$class->showConstant();
echo $class::constant."\n"; // As of PHP 5.3.0
?>`

Example #2 Static data example

`<?php
class foo {
// As of PHP 5.3.0
const bar = <<<'EOT'
bar
EOT;
}
?>`

Unlike heredocs, nowdocs can be used in any static data context.

> Note: Nowdoc support was added in PHP 5.3.0.

Static Keyword
Class Abstraction
Classes and Objects (PHP 5)
PHP Manual