Each site has a Tour, a Help Center and meta sites having faq where the site's purpose, workings and features of the Stack Overflow and Stack Exchange system are explained. Also, there is FAQ for Stack Exchange sites.
Most of the content doesn't include hard rules; instead, they are written as guidance and provide instructions about how it's intended that each community works and how to use the system features. Tours, help center articles, faq and moderator-faq explain the rules.
The tour, the Help Center homepage and some help articles can be customized to fit each community's needs, but most content is the same. Some might have variations to fit the community vocabulary according to their audience based on the work of their core community and under the guidance of the Community Managers.
Is there a tag for the Stack Overflow and Stack Exchange sites' posts about the standard rules for all sites and their enforcement instruments/implementation?