其实，正则表达式是XPATH2.0定义的，暂且放在XSLT里说吧。

还是举例来说正则表达式的用法吧。

XML源文件任意，XSLT文件：

<?xml version='1.0'?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
            xmlns:xs="http://www.w3.org/XMLSchema">
<xsl:template match="/">
    <xsl:variable name="file" select="'aa.txt'"/>
    <xsl:variable name="string" select="unparsed-text($file,ISO-8859-1)" />
    <xsl:analyze-string select="$string" regex="\n" >
        <xsl:non-matching-substring>
            <row>
            <xsl:analyze-string select="." regex='("([^"]*)")|([^,]+)'>
                <xsl:matching-substring>
                    <cell>
                    <xsl:value-of select="regex-group(2)"/>
                    <xsl:value-of select="regex-group(3)"/>
                    </cell>
                </xsl:matching-substring>
            </xsl:analyze-string>
            </row>
        </xsl:non-matching-substring>
    </xsl:analyze-string>
</xsl:template>
</xsl:stylesheet>

摘自XSLT2.0 porgrammer's reference(稍有改动)。

aa.txt的内容：

123,"Mary Jones","IBM","USA",1997-05-14
423,"Barbara Smith","General Motors","USA",1996-03-12
6721,"Martin McDougall","British Airways","UK",2001-01-15
830,"Jonathan Perkins","Springer Verlag","Germany",2000-11-17
得到输出结果：

         <cell>123</cell>

         <cell>Mary Jones</cell>

         <cell>IBM</cell>

         <cell>USA</cell>

         <cell>1997-05-14</cell>

        <cell>423</cell>

        <cell>Barbara Smith</cell>

         <cell>General Motors</cell>

        <cell>USA</cell>

        <cell>1996-03-12</cell>

        <cell>6721</cell>

        <cell>Martin McDougall</cell>

        <cell>British Airways</cell>

        <cell>UK</cell>

        <cell>2001-01-15</cell>

        <cell>830</cell>

       <cell>Jonathan Perkins</cell>

        <cell>Springer Verlag</cell>

        <cell>Germany</cell>

        <cell>2000-11-17</cell>

我们可以看到寻找与regex匹配的字符串的过程是：首先从input的第一个字符开始，看能否找到，如果找到了，那么就截取该匹配字符，然后从后面的字符开始，再次寻找，如果未找到，就将第一个字符确定为不匹配字符，然后从第二个字符开始寻找，一直到查找完所有字符。

原来的XSLT文件正则表达式匹配的模式为：