Because in PHP, some predefined constants are case-insensitive?

Question

Because, in the PHP, some predefined constants are case-insensitive (do not differentiate capital letters from minuscules) and others are not?

Example 1:

echo __FILE__; // index.php

echo __file__; // index.php

echo __fiLE__; // index.php

Example 2:

echo PHP_EOL; \n

echo php_eol; // Use of undefined constant php_EOL - assumed 'php_eol' 

echo php_EOL; // Use of undefined constant php_EOL - assumed 'php_EOL' 

As you can see, in the last case there is an error, in the first case there is no error!

Answer 1

Because it is possible to store constants case-insensitive see in the documentation Link

If set to TRUE, the Constant will be defined case-insensitive. The default behavior is case-sensitive; i.e. CONSTANT and Constant represent Different values.

Translation: If it is set to TRUE, the constant will be defined case-insensitive. The default behavior is case-sensitive; that is, constant and CONSTANT represent different values.

Note: Case-insensitive constants are stored as Lower-case.

Translation: case-insensitive constants are stored in lower case.

Soon it is possible that:

__FILE__; 

__file__;

__fiLE__;

Have the same value

Constant creation command (One of them is possible to create constants with the word const).

define ('CONSTANTE' , 12, true);
define ('CONSTANTe' , 12);