constant with a case-sensitive name

Question

case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false;

The example below creates a constant with a case-sensitive name:
<?php
define("MSG", "Hi SoloLearners!");
echo MSG;
?>
out put
Hi SoloLearners!
<?php
define("MSG", " Hi SoloLearners!", true);
echo msg;
?>

out put
Hi SoloLearners!
Difference between these two not clear.
Please make the concept clear in simple words. I referred to comment section but concept is not clear yet.

Answer 1

Case-sensitive means "Msg" and "MSG are not the same constant

In first example: if u do "echo Msg" it will throw errors as u have declared case insensitive to false so u have to type the constant name exactly as u did it wil delcaring it

while in second example case-insensitive is set to true so that's why u can also call it by using msg,Msg or MSg (doesnt matter)