What happens when group names get dashes underscores or other characters

In particular groupd with underscores are now ambiguous

Also what happens when the same group name come up in different order

We currently add all markers to a set, then sort them and join with _... I think this covers all cases correctly? Or do you have an example where this would cause problems?

1. The underscore is just to join them, so it would form something like this: group_1 + group_2 = group_1_group_2.

2. If we want to have a unique separator to retrieve the original groups we can, but the marks still exist in the item, i just change the nodeid in this case. In any case, we can choose some other one, like "::".

3. I check if the name already exists, so every mark is unique and then sorted. Just seen nico changed to a set, neat!

The logic for getting the name of the mark seems involved enough to make it a function

A fun hack would be

def group_name_of(name,*k,**kw):
  return name

groups = {group_name_of(*mark.args, **mark.kwargs) for mark in item.iter....}