Using Heredoc with multiple lines is not working

Question

I was testing a simple assignment of a variable using Heredoc, but when I try to echo it nothing shows up

<?php
$varable = <<<LINES
1st line
2nd line
LINES;
echo "<script>alert(\"$varable\")</script>";
?>

But when I try to run it with only 1 line, it works correctly:

<?php
$varable = <<<LINES
1st line
LINES;
echo "<script>alert(\"$varable\")</script>";
?>