string() transforms its argument into string : string « XSLT stylesheet « XML Tutorial

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2. XSLT stylesheet
3. string

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <number>9</number>
    <number>0</number>
    <number>-9</number>
    <number/>
</data>
File: Transform.xslt

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:variable name="A" select="number(//number[1])"/>
    <xsl:variable name="B" select="number(//number[2])"/>
    <xsl:variable name="C" select="number(//number[3])"/>
    <xsl:variable name="D" select="number(//number[4])"/>
    <xsl:template match="/">
      <Paragraph>
        <xsl:value-of select="string(number($A))"/>
      </Paragraph>
      <Paragraph>
        <xsl:value-of select="string(number($D))"/>
      </Paragraph>
      <Paragraph>
        <xsl:value-of select="$A"/>
        <xsl:text>/</xsl:text>
        <xsl:value-of select="$B"/>
        <xsl:text> = </xsl:text>
        <xsl:value-of select="string($A div $B)"/>
      </Paragraph>
      <Paragraph>
        <xsl:value-of select="$C"/>
        <xsl:text>/</xsl:text>
        <xsl:value-of select="$B"/>
        <xsl:text> = </xsl:text>
        <xsl:value-of select="string($C div $B)"/>
      </Paragraph>
      <Paragraph>
        <xsl:value-of select="$B"/>
        <xsl:text>/</xsl:text>
        <xsl:value-of select="$B"/>
        <xsl:text> = </xsl:text>
        <xsl:value-of select="$B div $B"/>
      </Paragraph>
    </xsl:template>
</xsl:stylesheet>

Output:

<?xml version="1.0" encoding="UTF-8"?><Paragraph>9</Paragraph><Paragraph>NaN</Paragraph><Paragraph>9/0 = INF</Paragraph><Paragraph>-9/0 = -INF</Paragraph><Paragraph>0/0 = NaN</Paragraph>