How to delimit a variable name in a string

Question

I want to set the attribute ref_id with "_0" suffixed, but

<xsl:attribute name="ref_id" select="$id_0" />

is parsed as variable name: id_0, not variable name id, plus string _0.

How to I nail this one down?

Thanks!

Answer 1

<xsl:attribute name="ref_id" select="concat($id, '_0')" />

Answer 2

<xsl:attribute name="ref_id"><xsl:value-of select="$id"/>_0</xsl:attribute>

Answer 3

And of course if the xsl:attribute is a child of a literal result element then you can do

<e ref_id="{$id}_0">