My specific task is writing a jFusion bridge, between Joomla! and XF, using J! as the master, and XF as the slave. So users are created and modified in J!, and changes are applied to XF via the bridge plugin. The code runs on the J! side, so modifications are currently done by poking around directly in the xf_ tables, not through the XF API.
[Yes, I know, I shouldn't do that. And at some point I'll work out how to instantiate XF inside a J! system plugin, and actually do it "the right way" by calling the XF functions to do all this. But for now, it is what it is. I inherited this code from the original author because I need it working "now" on my site, and I don't have time to do a bottom up rewrite.]
So my question is ... when adding XF users and setting their primary and secondary memberships, or when editing existing users to change their secondary group memberships, do I even need to worry about permission combinations?
What I'm doing at the moment is, on user creation I don't do anything. On user edit, I look to see if there is an xf_permission_combination row which matches the userid being modified, and their pre-change membership list, and if so, I modify it to change the group memberships to the new list.
This is just a wild guess at what needs to happen, now that I realize I actually have no real clue what the permission combinations are for.
TIA for any help.