<?php
$string = "some text (a(b(c)d)e) more text";
if(preg_match("http://(([^()]+|(?R))*/)/",$string,$matches)) {
echo "<pre>"; print_r($matches); echo "</pre>";
}
?>

Array
(
[0] => (a(b(c)d)e)
[1] => e
)

"http://(([^()]+|/(([^()]+|/(([^()]+)*/))*/))*/)/"

"http://(([^()]+|(?R))*/)/"

<?php
$string = "some text (a(b(c)d)e) more text";
if(preg_match("/((?:[^()]+|(?R))*)/",$string,$matches))
{
echo "<pre>"; print_r($matches); echo "</pre>";
}
?>
產生的結果相同:

Array
(
[0] => (a(b(c)d)e)
)

<?php
$string = "some text (a(b(c)d)e) more text";
if(preg_match("/((?>[^()]+|(?R))*)/",$string,$matches))
{
echo "<pre>"; print_r($matches); echo "</pre>";
}
?>