xml – 是否可以在xslt样式表中使用Dynamic xPath表达式？

我想在xpath表达式中使用xslt参数的值.具体来说,作为< xsl：if表达式中not()调用的一部分.

<xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <!-- my_param contains a string '/foo/bar',passed in from ant -->
    <!-- the 'no' is just a default value -->
    <xsl:param name="my_param">no</xsl:param>
    <xsl:variable name="var_myparam" select="$my_param" />
    <!-- ... -->

    <!-- this works -->
    <xsl:if test="not(/foo/bar)" /> <!-- expression returns boolean true -->
        <!-- ... -->
    </xsl:if>

    <!-- I can't figure out how to do this the right way -->
    <!-- None of these appear to work -->
    <xsl:if test="not($var_myparam)" /> <!-- expression returns boolean false -->
        <!-- ... -->
    </xsl:if>       
    <xsl:if test="not({$var_myparam})" /> <!-- complains required attribute 'test' is missing -->
        <!-- ... -->
    </xsl:if>       
    <xsl:if test="not({$myparam})" />   <!-- complains required attribute 'test' is missing -->
        <!-- ... -->
    </xsl:if>       
    <xsl:if test="not($myparam)" />     <!-- expression returns boolean false -->
        <!-- ... -->
    </xsl:if>       

</xsl:transform>

我有点不清楚在xslt样式表中创建动态xpath表达式的正确语法是什么.对于参数,变量以及两者的扩展方式之间的差异,我也有点模糊.例如,有了参数,我知道有时我需要括号,有时我不需要.

<!-- when creating an element,it seems I need brackets -->
<xsl:element name="{$my_param}" />

<!-- when selecting an element value for the output stream,no brackets are needed -->
<xsl:value-of select="$my_param"/>

任何一般/特定的帮助将不胜感激.

查看 http://www.exslt.org/. 具体来看动态：评估模块.