Hello David,

> I want to apply the function sum() but only when tagID = FA40.

use the key() function:

<xsl:key name="tags" match="tag" use="tagID"/>

	<xsl:template match="/">
		<xsl:value-of select="sum(key('tags','FA40')/tagF/tagG)"/>
	</xsl:template>

Kind regards,
Ismaël


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