php - Why Superglobals can't be printed in double quotes?

$x = "world";
echo "hello $x";
echo "hello $GLOBALS['x']";
?>

In the above code the first statement prints hello world but second doesn't print anything.Why superglobals are not accessible in double quotes?

Answer

It's not that super globals can't it's that you can't access items in an array in the string. If you did the following it'll work fine.

echo "hello {$GLOBALS['x']}";