PHP 关键词
__halt_compiler() abstract and array() as
break callable (as of PHP 5.4) case catch class
clone const continue declare default
die() do echo else elseif
empty() enddeclare endfor endforeach endif
endswitch endwhile eval() exit() extends
final finally (从PHP 5.5开始) for foreach function
global goto (从PHP 5.3开始) if implements include
include_once instanceof insteadof (从PHP 5.4开始) interface isset()
list() namespace (从PHP 5.3开始) new or print
private protected public require require_once
return static switch throw trait (从PHP 5.4开始)
try unset() use var while
xor yield (从PHP 5.5开始)      
编译时常量
__CLASS__ __DIR__ (从PHP 5.3开始) __FILE__ __FUNCTION__ __LINE__
__METHOD__ __NAMESPACE__ (从PHP 5.3开始) __TRAIT__ (从PHP 5.4开始)