The operator '!=' returns false when one operand doesn

Hi All,

We have an issue with the XPath '!=' operator that has
a strange behavior when one of its operand doesn't
exist in the instance document. It returns 'false"
when you would expect "true" or some kind of exception
to be raised.

Sample stylesheet:
------------------
<?xml version="1.0" encoding="UTF-8"?>
<xsl:transform version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
	<xsl:template match="/">
		<data>
			<xsl:value-of select="/data/a != /data/b"/>
		</data>
	</xsl:template>
</xsl:transform>

Instance:
---------
<?xml version="1.0"?>
<data>
	<a>10</a>
</data>

This transformation will return 'false'.
If you add <b>11</b> under element a, or even an empty
<b/>, the result is becoming 'true'.

Could somebody explain me why we get such a result
(with MSXML 4.0 as well as Xalan)?
Is there a simple way, extension function or XPath
expression to would make this work as "expected" (true
is one of this operand doesn't exist)?

Thanks for your help!
Jerome.



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