php有哪些类型是不区分大小写？

 <?php
 function show(){
 echo "Hello World";
 }

<?php
 class cls{
 static function func(){
 echo "hello world";
 }
 }
 Cls::FunC(); //输出hello world

 <?php 
 echo __line__; //输出 2 
 echo __LINE__; //输出 3

<?php
 $a = null;
 $b = NULL;
 $c = true;
 $d = TRUE;
 $e = false;
 $f = FALSE;
 var_dump($a == $b); //输出 boolean true
 var_dump($c == $d); //输出 boolean true
 var_dump($e == $f); //输出 boolean true

<?php
    function bbb(){
        echo &#39;abc&#39;;
    }
    function BBB(){
        echo "Abc";
    }
?>