Try changing ^\[$ to ^\[\s*.

I don't know if the following is valid:

$string = '
[foobar]
[
this is a list
of things
that are in a list
]
blah blah later after-list text
';
[download]

but my guess is that if it is valid then i doubt the change sauoq suggested will return the wanted results. what you probably want is to change ^\[$ to ^\[\s*?\n (where then the [ can only be followed by "optional whitespace" and then a newline.)

-enlil