## 關鍵字 以及 True/False/Null * PHP所有 關鍵字**必須**全部小寫。 <table class="doctable table"> <caption><strong>PHP Keywords</strong></caption> <tbody class="tbody"> <tr><td> <span class="function">__halt_compiler()</span></td><td> abstract</td><td> and</td><td> <span class="function">array()</span></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> <span class="function">die()</span></td><td> do</td><td> <span class="function">echo</span></td><td> else</td><td> elseif</td></tr> <tr><td> <span class="function">empty()</span></td><td> enddeclare</td><td> endfor</td><td> endforeach</td><td> endif</td></tr> <tr><td> endswitch</td><td> endwhile</td><td> <span class="function">eval()</span></td><td> <span class="function">exit()</span></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> <span class="function">include</span></td></tr> <tr><td> <span class="function">include_once</span></td><td> instanceof</td><td> insteadof (as of PHP 5.4)</td><td> interface</td><td> <span class="function">isset()</span></td></tr> <tr><td> <span class="function">list()</span></td><td> namespace (as of PHP 5.3)</td><td> new</td><td> or</td><td> <span class="function">print</span></td></tr> <tr><td> private</td><td> protected</td><td> public</td><td> <span class="function">require</span></td><td> <span class="function">require_once</span></td></tr> <tr><td> <span class="function">return</span></td><td> static</td><td> switch</td><td> throw</td><td> trait (as of PHP 5.4)</td></tr> <tr><td> try</td><td> <span class="function">unset()</span></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**必須**全部小寫。