[Zope] calling external script from index_html

Hello list, just getting going and already belly-flopped at the first hurdle. In a folder holding the external method object, an index_html referencing it via <dtml-val myscript_func> does not appear to run the script, while a dtml method created in the same folder and making the same reference does run ok. I tried moving the external method object into a higher level folder in case it somehow was not in scope, but to no avail. What is the correct way to make external scripts available to index_html's? Cheers, Chris Quinn