These words cannot be used to name a class, interface or a trait. These words are also prohibited from being used in namespaces. Some of the words are reserved to enable future PHP features without breaking backward compatibility.
| int (as of PHP 7) | float (as of PHP 7) | bool (as of PHP 7) | string (as of PHP 7) |
| true (as of PHP 7) | false (as of PHP 7) | null (as of PHP 7) | resource (as of PHP 7) |
| object (as of PHP 7) | mixed (as of PHP 7) | numeric (as of PHP 7) |