[Zope] DTML Document ids

[Giuseppe Bonelli]

Can someone explain to me why in the following code the line starting
with * outputs a null string and the line starting with ** outputs the
correct id of the DTMLDocument object ?

<dtml-var standard_html_header>
<dtml-in expr="objectItems('DTML Document')" prefix="sequence">
*<dtml-var "sequence_item.id"><br/>
**<dtml-var id><br/>
</dtml-in>
<dtml-var standard_html_footer>

TIA

__peppo