And how, exactly, does this relate to sourdough?

- Steve Brandt

Are you suggesting that all postings here directly address sourdough
and nothing but?

Despite what I would suggest is a lack of support for the existence of
such a norm (let alone some firm constraint), the relationship is as
follows:

As evidenced in a number of recent postings, many sourdough bread
bakers participating in this group grind their own grains, as do a
number of published writers on the subject. Some of these bakers that
grind their own grains for sourdough breads also grind grains for
their non-sourdough baking, including some that rave at length about
the wonders of freshly ground corn for making cornbread. This brief
set of links seems to make the question relevant to the knowledge
and/or interests of this community of users.