<xh:html xmlns:xf="http://www.w3.org/2002/xforms"
         xmlns:ev="http://www.w3.org/2001/xml-events"
         xmlns:xh="http://www.w3.org/1999/xhtml">
    <xh:head>
        <xf:model>
            <xf:instance>
                <instance>
                    <value/>
                    <show-help>false</show-help>
                    <help/>
                </instance>
            </xf:instance>
            <xf:bind ref="value" relevant="../show-help = 'true'"/>
        </xf:model>
    </xh:head>
    <xh:body>
        <xf:trigger>
            <xf:label>Toggle</xf:label>
            <xf:setvalue ev:event="DOMActivate" ref="show-help" value="if (. = 'true') then 'false' else 'true'"/>
        </xf:trigger>
        <xh:br/>
        <xf:input ref="help">
            <xf:label>Help message:</xf:label>
        </xf:input>
        <xh:br/>
        <xf:input ref="value">
            <xf:label>Value:</xf:label>
            <xf:help ref="../help"/>
        </xf:input>
    </xh:body>
</xh:html>