function ubb($Text) { 
  $Text=htmlspecialchars($Text); 
  $Text=ereg_replace("rn","br",$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); 
  $Text=preg_replace("/[sup](.+?)[/sup]/is","sup\1/sup",$Text); 
  $Text=preg_replace("/[sub](.+?)[/sub]/is","sub\1/sub",$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","blockquotefont size='2' face='Courier New'quote:/fonthr\1hr/blockquote", $Text); 
  $Text=preg_replace("/[code](.+?)[/code]/is","blockquotefont size='2' face='Courier New'code:/fonthr color='lightblue'i\1/ihr color='lightblue'/blockquote", $Text); 
  $Text=preg_replace("/[sig](.+?)[/sig]/is","div style='text-align: left; color: darkgreen; margin-left: 5%'brbr--------------------------br\1br--------------------------/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