Wrapping on Characters Other Than Space?

I checked the below page but unfortunately there wasn't an answer to my 
question

http://www.sagehill.net/docbookxsl/ProgramListings.html

I'd like to be able to break program listing lines/command lines on 
characters other than "space", since in some lines, there aren't any. Is 
there a way of specifying other characters to break on, such as a comma?

Thanks,

-pm