正则表达式 - PHP正则 #info/list#u 为什么反斜杠“/” 可以不用转义

<code>php</code><code><?php 
$pattern = '#^info/(?P<type>(area|cat))-(?P<v1>\d+)-(?P<v2>\d+)-(?P<v3>\d+)/(?P<page>\d+)/$#u';
$str = 'info/area-19-0-0/40/';
preg_match($pattern,$str,$matches);
print_r($matches);

</code>

<code>Array
(
    [0] => info/area-19-0-0/40/
    [type] => area
    [1] => area
    [2] => area
    [v1] => 19
    [3] => 19
    [v2] => 0
    [4] => 0
    [v3] => 0
    [5] => 0
    [page] => 40
    [6] => 40
)
</code>

<code>php</code><code><?php 
$pattern = '#^info/(?P<type>(area|cat))-(?P<v1>\d+)-(?P<v2>\d+)-(?P<v3>\d+)/(?P<page>\d+)/$#u';
$str = 'info/area-19-0-0/40/';
preg_match($pattern,$str,$matches);
print_r($matches);

</code>

<code>Array
(
    [0] => info/area-19-0-0/40/
    [type] => area
    [1] => area
    [2] => area
    [v1] => 19
    [3] => 19
    [v2] => 0
    [4] => 0
    [v3] => 0
    [5] => 0
    [page] => 40
    [6] => 40
)
</code>