Re: understanding generate-id and node-equality [XSLT

using XSLT 1.0 and Saxon 6.5.5 I'm wondering whats the actual difference
between

<xsl:key name="child-key" match="child" use="parent::*"/>

<xsl:template match="parent" >
        <xsl:variable name="childs" select="key('child-key', parent::*)"/>
        ...
</xsl:template>

and

<xsl:key name="child-key" match="child" use="generate-id(parent::*)" />

<xsl:template match="parent" >
        <xsl:variable name="childs" select="key('child-key',
generate-id(parent::*))" />
        ...
</xsl:template>

I think I know what generate-id does,

but what is tested when I use the
former expression?

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