To make things even more clear (I hope), I'll just add that you can pass modifiers to qr, just like you can for normal regexes, like this:

$re = qr/<!--.*?-->/s;
print $re;
[download]

which prints

  (?s-xim:<!--.*?-->)
[download]

That is: /s enabled, and /x, /i and /m disabled.