"\'" in PHP

$ cat test.php
<?php
$string = "O\'Reilly";
echo $string, "\n";
?>
$ php test.php
O\'Reilly

That's documented but not expected.

Languages like Perl, Python, Ruby, Common Lisp, C, Scheme, OCaml, Erlang, Haskell, Tcl, JavaScript, etc. print the expected "O'Reilly".

One small stone you can stumble on.