Case Sensitivity

Case sensitivity refers to the way PHP retrieves names when it looks for a definition: is it in a case-sensitive way, or case insensitive.

The case insensitive named structures are:

• classes

• enumerations

• functions

• interfaces

• magic methods

• methods

• namespaces

• php keywords

• traits

The case sensitive named structures are:

• class constants

• constants (since PHP 8.0)

• array index

• properties

• variables

<?php

// two distinct variables
$x = 1;
$X = 2;

// two identical calls
foo();
FOO();

?>