[xsl] NaN and Infinity in format-number

[Jack Matheson <jack@xxxxxxxxxxxxxx>]

In the following stylesheet:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/ 
Transform">
  <xsl:template match="/">
    1: <xsl:value-of select="format-number(0.0 div 0.0, '(#)')"/>
    2: <xsl:value-of select="format-number(1.0 div 0.0, '(#)')"/>
  </xsl:template>
</xsl:stylesheet>

...I see interesting results in Saxon 6 and Xalan 2.6:

    1: NaN
    2: (Infinity)

I was expecting either parenthesis around both values or no  
parenthesis at all. Is this a result of the XSLT 1.0 processors using  
DecimalFormat in the JDK?
Is this the conforming XSLT 1.0 behavior?

I noticed Saxon 8 puts parenthesis around both values. Is this an an  
XSLT 2.0 action?

Any help is appreciated!

-Jack