➤ PHP is partially case-sensitive. PHP constructs, function names, class names are case-insensitive, whereas variables are case-sensitive If we define a variable

$name = "Mads";

then we must need to use $name. $NAME will not work.

$name = "Mads";
echo $NAME; // output: error

If we defined function name in lowercase, but calling them in uppercase it will work. For instance, If we define function sum() {} then calling SUM() will also work.

function sum () {
	echo "10 + 10 = 20 \n";
}
SUM(); // output: 10 + 10 = 20