Whats that: false and false = true!?

[Peter Nabbefeld]

Hello!

This
        <xsl:message>Button1[extended] = <xsl:value-of
select="$button1"/></xsl:message>
        <xsl:message>Button2[extended] = <xsl:value-of
select="$button2"/></xsl:message>
        <xsl:message>Button3[extended] = <xsl:value-of
select="$button3"/></xsl:message>
        <xsl:message>Buttons-extended  = <xsl:value-of
select="boolean($button1) and boolean($button2) and
boolean($button3)"/></xsl:message>

results in this output:
        Button1[extended] = false
        Button2[extended] = false
        Button3[extended] = false
        Buttons-extended  = true

Could anybody please tell me, why? BTW: My first try was without the
"boolean"

Kind regards

Peter Nabbefeld