DOCBOOK-APPS: (openjade + dsssl) changing <orderedlistnumeration="loweralpha"> rendering

Hi,

is there anybody knows, how can i change the behavour of the 
numbering of lists in case of "loweralpha". I need the following
style:
a) first list item
b) second list item

i examined the whole stylesheet package (dsssl 1.76b+) but i didn't
find anything except some funcion-call(?) format-number, but it's
definition seems not to exist anywhere.

Thanks for any hints:
G.