2.5. 关键字以及 True/False/Null · PHP PSR-2 代码风格规范

## 关键字以及 True/False/Null * PHP所有关键字**必须**全部小写。 <table class="doctable table"> <caption>PHP Keywords</caption> <tbody class="tbody"> <tr><td> __halt_compiler()</td><td> abstract</td><td> and</td><td> array()</td><td> as</td></tr> <tr><td> break</td><td> callable (as of PHP 5.4)</td><td> case</td><td> catch</td><td> class</td></tr> <tr><td> clone</td><td> const</td><td> continue</td><td> declare</td><td> default</td></tr> <tr><td> die()</td><td> do</td><td> echo</td><td> else</td><td> elseif</td></tr> <tr><td> empty()</td><td> enddeclare</td><td> endfor</td><td> endforeach</td><td> endif</td></tr> <tr><td> endswitch</td><td> endwhile</td><td> eval()</td><td> exit()</td><td> extends</td></tr> <tr><td> final</td><td> finally (as of PHP 5.5)</td><td> for</td><td> foreach</td><td> function</td></tr> <tr><td> global</td><td> goto (as of PHP 5.3)</td><td> if</td><td> implements</td><td> include</td></tr> <tr><td> include_once</td><td> instanceof</td><td> insteadof (as of PHP 5.4)</td><td> interface</td><td> isset()</td></tr> <tr><td> list()</td><td> namespace (as of PHP 5.3)</td><td> new</td><td> or</td><td> print</td></tr> <tr><td> private</td><td> protected</td><td> public</td><td> require</td><td> require_once</td></tr> <tr><td> return</td><td> static</td><td> switch</td><td> throw</td><td> trait (as of PHP 5.4)</td></tr> <tr><td> try</td><td> unset()</td><td> use</td><td> var</td><td> while</td></tr> <tr><td> xor</td><td> yield (as of PHP 5.5)</td><td></td><td></td><td></td></tr> </tbody> </table> * 常量true、false和null也**必须**全部小写。