variables in parents : xsl

Hello,

This maybe isn't entirely the correct place to ask.
But how can I access variables from parents in xsl?

Eg.: I have a custom list where the list itself has an id. Now I want to be 
able to let every listitem now the id of that list.

<xsl:template match="customlist">
  <xsl:variable name="listid">
    <xsl:value-of select="generate-id()"/>
  </xsl:variable>
</xsl:template>

<xsl:template match="customlist/listitem">
  <xsl:copy-of select="$listid"/>
</xsl:template>

Thanks,

Wim Lemkens