if you are using muenchian grouping, the analogue of current-group() is
key()


<xsl:for-each-group select="//*[count(ancestor-or-self::*) = 3 
group-by="@name">
  <xsl:value-of select="sum(current-group()/descendant::value)"/>


<xsl:key name="k" match="/*/*/*" use="@name"/>

<xsl:for-each
select="/*/*/*[generate-id()=generate-id(key('k',@name))]">
    <xsl:value-of select="sum(key('k',@name)/descendant::value)"/>


David

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