Regular Expressions-PHP regular #info/list#u why backslash "/" can not be escaped

PHP-generated regular, to #Beginning #uThe end, why the inside /Backslashes are not escaped into \/

php
  
   (area|cat))-(?P
  
   
    
   \d+)-(?P
   
    
     
    \d+)-(?P
    
     
      
     \d+)/(?P
     
      
       
      \d+)/$#u';$str = 'info/area-19-0-0/40/';preg_match($pattern,$str,$matches);print_r($matches);
     
      
    
     
   
    
  
   

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)

Reply content:

PHP generated regular, at the # beginning #u of the end, why the inside of the backslash does / not have to escape into\/

php
  
   (area|cat))-(?P
  
   
    
   \d+)-(?P
   
    
     
    \d+)-(?P
    
     
      
     \d+)/(?P
     
      
       
      \d+)/$#u';$str = 'info/area-19-0-0/40/';preg_match($pattern,$str,$matches);print_r($matches);
     
      
    
     
   
    
  
   

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)

Because its regular delimiter is a # number, it / does not need to be escaped.

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