[GiNaC-list] differentiating with respect to a variable in a list

Hi everyone, I have a small question. I'd like to make a function with a list as one argument and be able to take derivatives with respect to the variables encased in the list. The only such example among the built-in functions seems to be Li for lists in the second variable, but in this case all but the first element of that list seem to be ignored. Is there an example I've missed that I could look at, or some place that documents how this works? Thanks for your time. Karen