如何用php 正则表达式，提取html内容

[这题要怎么做]

</div>
<table class="xmu_table_class" id="jbxx_f3288" align="center" width="100%" >
<tr>
<th width="8%">
学号:

</th>
<td width="18%">
<span class="span_unedit_fix">233201222023523</span>
</td>
<th width="8%">
姓名:

</th>
<td width="18%">
<span class="span_unedit_fix">李四</span>

</td>

<th width="8%">
姓名拼音:

</th>
<td width="18%">
<span class="span_unedit_fix">Li Si</span>

</td>
上面是某网页的源代码，要用php 正则表达式，提取学号，姓名 ，姓名拼音:怎么写php的代码

[zhangsheng_1992]

<?php
header("content-type:text/html;charset=utf-8");
$str = '</div>
<table class="xmu_table_class"   id="jbxx_f3288" align="center" width="100%" >
<tr>
<th width="8%">
学号:

</th>
<td width="18%">
 <span class="span_unedit_fix">233201222023523</span> 
</td>
<th width="8%">
姓名:

</th>
<td width="18%">
<span class="span_unedit_fix">李四</span>

</td>

<th width="8%">
姓名拼音:

</th>
<td width="18%">
<span class="span_unedit_fix">Li Si</span>

</td>';
$reg = '/<span.*>(.*)<\/span>/';
preg_match_all($reg, $str, $result);
print_r($result);
?>

[xuzuning]

$s =<<< TXT
</div>
<table class="xmu_table_class"   id="jbxx_f3288" align="center" width="100%" >
<tr>
<th width="8%">
学号:

</th>
<td width="18%">
 <span class="span_unedit_fix">233201222023523</span> 
</td>
<th width="8%">
姓名:

</th>
<td width="18%">
<span class="span_unedit_fix">李四</span>

</td>

<th width="8%">
姓名拼音:

</th>
<td width="18%">
<span class="span_unedit_fix">Li Si</span>

</td>
TXT;

preg_match_all('#<th\s.+?>(.+?)</th>#is', $s, $m);
print_r($m[1]);

Array ( [0] => 学号: [1] => 姓名: [2] => 姓名拼音: )