Null output from stylesheet

A root-matching template whose only children are xsl:variable declarations produces no output. The variables are computed but nothing is ever written to the result tree, which is almost certainly a logic error.

Incorrect:

<xsl:template match="/">
  <xsl:variable name="heading" select="title"/>
  <xsl:variable name="count" select="count(item)"/>
</xsl:template>

Correct:

<xsl:template match="/">
  <xsl:variable name="heading" select="title"/>
  <xsl:variable name="count" select="count(item)"/>
  <h1><xsl:value-of select="$heading"/></h1>
  <p>Items: <xsl:value-of select="$count"/></p>
</xsl:template>