should there be an error condition with XPATH function

having some problems interpreting what is expected behavior with the
following XSLT.

xml
<test>1</test>

xslt
<xsl:template match="/">
    <xsl:apply-templates select="."/>
</xsl:template>

<xsl:template match="test">
    <xsl:value-of select="contains(test, $somevariable)"/>
</xsl:template>

note that $somevariable has not been declared with either xsl:param or
xsl:variable.

in http://www.w3.org/TR/xpath spec it is clear that the contains()
function should return a false condition and I cant find anything to the
contrary that would say that this should throw an error (as it doesnt in
Firefox XSLT processor). Note I havent tried any other variations with
respect to functions or templates.

Any comments, guidence etc...would be appreciated (being lazy any
comments re XSLT / XPATH 2.0 would be great as well).

cheers, Jim Fuller