ip-the meaning of this regular expression?

ipphp Regular Expressions

The whole function is to get the real IP,

 function Real_ip () {Static $realip = NULL;    if ($realip!== NULL) {return $realip;  } if (Isset ($_server)) {if (Isset ($_server[' http_x_forwarded_for ')) {$arr = explode (', ',            $_server[' http_x_forwarded_for ');                /* Take the first non-unknown valid IP string in x-forwarded-for */foreach ($arr as $ip) {$ip = Trim ($IP);                    if ($ip! = ' Unknown ') {$realip = $ip;                Break }}} elseif (Isset ($_server[' http_client_ip ')) {$realip = $_server[' http_cli        Ent_ip ']; } else {if (Isset ($_server[' remote_addr ')) {$realip = $_server[' REMO            Te_addr '];            } else {$realip = ' 0.0.0.0 '; }}}} else {if (getenv (' http_x_forwarded_for ')) {$realip = getenv (' http_x_Forwarded_for ');        } elseif (getenv (' http_client_ip ')) {$realip = getenv (' http_client_ip ');        } else {$realip = getenv (' remote_addr '); }} preg_match ("/[\d\.")    {7,15}/", $realip, $ONLINEIP); $realip =!empty ($onlineip [0])?    $ONLINEIP [0]: ' 0.0.0.0 '; return $realip;}

Preg_match ("/[\d.") {7,15}/", $realip, $ONLINEIP); The regular expression here is a bit confused,
Why do numbers or dots repeat seven to 15 times?

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