The kind of rules the Washington Post article talks about, i.e., explicitly formulated rules that are supposed to regulate behavior but are not (yet) laws. The article contrasts this to "unwritten rules", by which they seem to mean social norms and/or conventions. Social norms are usually not explicitly formulated and codified and if they are, they still exist independently of that formulation insofar as they are internalized by a significant number of members of a group. They evolve organically out of actual social interactions.

How exactly they evolve, what distinguishes social norms from conventions, and their relation to institutions, these are highly controversial topics. I'd personally recommend Cristina Bicchieri's taxonomy and approach, but there are other theories out there. In any case, it seemed clear to me that the WP article didn't talk about social norms - you cannot just decide what social norm is to be in place, these evolve independently and can be more or less stable -, and the WP article doesn't talk about laws only either. It seems to be based on the idea that written codes that are not laws should complement laws and replace actual social norms as kind of guidelines of how to behave, and I reject this idea for many reasons, including many moral ones.

To summarize my reasons very briefly: Everybody has a right to be an asshole and not every undesirable or unwanted behavior is also immoral. I'm very unhappy about the apparent trend (which seems to mostly exist in the US only) of not being able to distinguish between criminal behavior, immoral behavior, generally undesirable behavior, and personally unwanted behavior. These are all different things and mixing them up leads to a lot of confusion.