自定义ubb代码,preg_replace()函数的一些代码

function ubb($Text) { 
  $Text=htmlspecialchars($Text); 
  $Text=ereg_replace("\r\n","<br>",$Text); 
  $Text=ereg_replace("\r","<br>",$Text); 
  $Text=nl2br($Text); 
  $Text=preg_replace("/\\t/is","  ",$Text); 
  $Text=preg_replace("/\[h1\](.+?)\[\/h1\]/is","<h1>\\1</h1>",$Text); 
  $Text=preg_replace("/\[h2\](.+?)\[\/h2\]/is","<h2>\\1</h2>",$Text); 
  $Text=preg_replace("/\[h3\](.+?)\[\/h3\]/is","<h3>\\1</h3>",$Text); 
  $Text=preg_replace("/\[h4\](.+?)\[\/h4\]/is","<h4>\\1</h4>",$Text); 
  $Text=preg_replace("/\[h5\](.+?)\[\/h5\]/is","<h5>\\1</h5>",$Text); 
  $Text=preg_replace("/\[h6\](.+?)\[\/h6\]/is","<h6>\\1</h6>",$Text); 

  $Text=preg_replace("/\[url\](http:\/\/.+?)\[\/url\]/is","<a href=\\1>\\1</a>",$Text); 
  $Text=preg_replace("/\[url\](.+?)\[\/url\]/is","<a href=\"http://\\1\">http://\\1</a>",$Text); 
  $Text=preg_replace("/\[url=(http:\/\/.+?)\](.)\[\/url\]/is","<a href=\\1>\\2</a>",$Text); 
  $Text=preg_replace("/\[url=(.+?)\](.)\[\/url\]/is","<a href=http://\\1>\\2</a>",$Text); 

  $Text=preg_replace("/\[img\](.+?)\[\/img\]/is","<img src=\\1>",$Text); 
  $Text=preg_replace("/\[color=(.+?)\](.+?)\[\/color\]/is","<font color=\\1>\\2</font>",$Text); 
  $Text=preg_replace("/\[size=(.+?)\](.+?)\[\/size\]/is","<font size=\\1>\\2</font>",$Text); 
  $Text=preg_replace("/\[sup\](.+?)\[\/sup\]/is","^\\1",$Text); 
  $Text=preg_replace("/\[sub\](.+?)\[\/sub\]/is","_\\1",$Text); 
  $Text=preg_replace("/\[pre\](.+?)\[\/pre\]/is","<pre>\\1</pre>",$Text); 
  $Text=preg_replace("/\[email\](.+?)\[\/email\]/is","<a href=\\1>\\1</a>",$Text); 
  $Text=preg_replace("/\[i\](.+?)\[\/i\]/is","<i>\\1</i>",$Text); 
  $Text=preg_replace("/\[b\](.+?)\[\/b\]/is","<b>\\1</b>",$Text); 
  $Text=preg_replace("/\[quote\](.+?)\[\/quote\]/is","<blockquote><font size='2' face='Courier New'>quote:</font><hr>\\1<hr></blockquote>", $Text); 
  $Text=preg_replace("/\[code\](.+?)\[\/code\]/is","<blockquote><font size='2' face='Courier New'>code:</font><hr color='lightblue'><i>\\1</i><hr color='lightblue'></blockquote>", $Text); 
  $Text=preg_replace("/\[sig\](.+?)\[\/sig\]/is","<div style='text-align: left; color: darkgreen; margin-left: 5%'><br><br>--------------------------<br>\\1<br>--------------------------</div>", $Text); 
return $Text; 
} 
function str($msg){
  global $admin;
  if(!$admin[html]) $msg=htmlspecialchars($msg);
  if($admin[ubb]) $msg=ubb($msg);
  $msg=nl2br($msg); #处理message
  $msg= str_replace("\n","",$msg); #处理message
  $msg= str_replace("\r","",$msg); #处理message
  return $msg;
}
function error($msg){
global $admin;
?>

中的
$Text=preg_replace("/\[h2\](.+?)\[\/h2\]/is","<h2>\\1</h2>",$Text); 

里面的 ("/\[h2](.+?)\[\/h2]/is","<h2>\\1</h2>",$text)

/\[h2](.+?)\[\/h2]/is  转化成 <h2>\\1</h2>

/\[h2](.+?)\[\/h2]/is  里面的 这些"/\(.+?)\ "之类的符号是怎么看的?是什么意思?
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\是转意，\本身是特殊符号，如果要作为普通字符就要用\来转意，就是说\\表示()也是特殊符号，所以要用\转意