Zimlet not showing up anything

[MacTI]

I'm writing my first Zimlet so that I can show up basic membership information when a member ID (one letter + 4 digits) is detected. So I did this :

<zimlet name="com_acaiq_zimlet_infomembre" version="0.46" description="Affiche les infos sur un membre">
<contentObject>
<matchOn>
<regex attrs="ig">(X1005)</regex>
</matchOn>
<toolTip>
<actionUrl method="get" target="http://staging.xxxxx.xxx/cgi-bin/WebObjects/ServeurCertification.woa/ra/formations/liste.xml" />
</toolTip>
</contentObject>
</zimlet>

liste.xml (REST service) returns :

<?xml version="1.0" encoding="UTF-8"?>
<FormParticipants type="FormParticipants">
<FormActivite type="FormActivite" id="9924">
<facHeurePrevue>09:00</facHeurePrevue>
<facDatePrevue>2010-08-01T00:00:00Z</facDatePrevue>
<formTypeActivite type="FormTypeActivite" id="467">
<ftaTitre>Formation obligatoire - loi 73</ftaTitre>
</formTypeActivite>
<formLieu type="FormLieu" id="1">
<flNom>Some place</flNom>
</formLieu>
</FormActivite>
</FormParticipants>

I do see, with Firebug and Apache logs, that the data is fetched from the REST service, but the tooltip only shows "undefined". I tried adding a XSLT file :

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html"/>
<xsl:template match="FormParticipants/FormActivite">
<div><b>ID: </b> <xsl:value-of select="id"/></div>
<xsl:choose>
<xsl:when test="@error != ''">
<div><b>Error: </b> <xsl:value-of select="@error"/></div>
</xsl:when>
<xsl:otherwise>
<div><b>Date prévue: </b> <xsl:value-of select="facDatePrevue"/></div>
<div><b>Heure prévue: </b> <xsl:value-of select="facHeurePrevue"/></div>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template match="text()|@*"/>
</xsl:stylesheet>

and in the definition file, I added :

<resource>membre.xsl</resource>

Still a nogo. I did modify the allowed domains list so that staging.xxxxx.xxx is allowed, so I don't know why it's not showing anything. I didn't find any JavaScripts error in Firefox console, and neither in mailbox.log.