List of Keywords

These words have special meaning in PHP. Some of them represent things which look like functions, some look like constants, and so on--but they're not, really: they are language constructs. You cannot use any of the following words as constants, class names, function or method names. Using them as variable names is generally OK, but could lead to confusion.

PHP Keywords
abstract (as of PHP 5) and array() as break
case catch (as of PHP 5) cfunction (PHP 4 only) class clone (as of PHP 5)
const continue declare default do
else elseif enddeclare endfor endforeach
endif endswitch endwhile extends final (as of PHP 5)
for foreach function global goto (as of PHP 5.3)
if implements (as of PHP 5) interface (as of PHP 5) instanceof (as of PHP 5)
namespace (as of PHP 5.3) new old_function (PHP 4 only) or private (as of PHP 5)
protected (as of PHP 5) public (as of PHP 5) static switch throw (as of PHP 5)
try (as of PHP 5) use var while xor
Compile-time constants
__CLASS__ __DIR__ (as of PHP 5.3) __FILE__ __LINE__ __FUNCTION__ __METHOD__
__NAMESPACE__ (as of PHP 5.3)
Language constructs
die() echo() empty() exit() eval()
include() include_once() isset() list() require()
require_once() return() print() unset()