Pertaining to the original request in #133 does it make sense to allow users to pass in custom key/val pairs to marks (via **kwargs or some other API) such that user defined collection and/or hook calling behaviour can be controlled/modified by the user based on their own inputs (maybe it's more relatable in the context of #151).
It would potentially look something like:
from pluggy import HookspecMarker
hookspec = HookspecMarker('blah')
@hookspec(historic=True, a_special_hook=True)
def my_special_hook(arg):
"""This hook is only collected in special cases."""
pass