Re: boolean(string(false())) is true - always?

<xsl:function name="dy:isFoo" as="xs:boolean">
    <xsl:param name="node" as="node()"/>
    <xsl:choose>
      <xsl:when test="$node[self::bar/@foo = 'x']">
            <xsl:value-of select="true()"/>
        </xsl:when>
        <xsl:otherwise>
            <xsl:value-of select="false()"/>
        </xsl:otherwise>
    </xsl:choose>
</xsl:function>

and changed that to the more elegant:

<xsl:function name="dy:isFoo" as="xs:boolean">
    <xsl:param name="node" as="node()"/>
    <xsl:sequence select="exists($node[self::bar/@foo = 'x'])"/>
</xsl:function>

BUT then I looked at my old code and said to myself: This could never have worked?!

Isn't xsl:value-of creating a text node, so in xsl:otherwise it creates 'false'. And if this is cast to boolean as the function requires, we should get true(), because the string is not empty?