<b>Lorem ipsum dolor</b> sit amet, "consectetur adipisicing elit"<br /><br />
<b>sed doeiusmod</b> tempor incididunt ut's labore et dolore magna's aliqua.

$string = "[custom_text]";
$string = '[custom_text]';

$string = <<<EOT
[custom_text]
EOT;

<?php
$string = "This string has 'single quotes'";
echo addcslashes($string, '"\');
?>

This string has 'single quotes'