Re my comments on the documentation page:
Yes, I got a bit confused, as I was trying to reverse-engineer the acceptable parameters, and draft us up some documentation in approximately the same format as the parent page. I was also using the documentation on the Frieze groups as hints on the semantics for the wallpaper group parameters. I left my "Bug" comment up there even after I realised I was wrong, as I wanted to think about it and return to it - thus the "D'Oh" comment. I think there is still a slight bug in that all other axes (e.g. in p4 etc) can have their axes offset, whereas pm can't. Also it would be nice if absence of all params defaults to all params=0 as it does in other cases.
I was too tired to think straight last night, and don't have time to think about it now.
Overall I think it is a nice implementation - pretty straightforward and flexible. I still haven't updated my sample code to use it, but will in time.