php class constant visibility

As of PHP7.1 visibility modifiers are allowed for class constants, in previous versions it's not possible to set the visibility of constants in a class. They're always public. See the comments at http://www.php.net/manual/en/language.oop5.constants.php for more information.

Update: visibility modifiers for constants have been added in PHP 7.1 (released 1st of December 2016). See the RFC : Support Class Constant Visibility.

The syntax looks like this:

class ClassName {
    private const PRIVATE_CONST = 0;
    protected const PROTECTED_CONST = 0;
    public const PUBLIC_CONST = 0;
}