[Zope] include/import module

[Allen Wallis]

Hi,
How do I import a module - I've been reading the DTML guide, and I would
like to use some of the functions described in the string module, but
how do use them - do I have to import the module (if so, how), or what
else. What I want to use is the following:
<dtml-if expr="lower(somestring)=='supplier'">

</dtml-if>
where lower is defined in the string module. I've also tried
string.lower(...) but that didn't seem to work.

thanks
Allen