[rmah]

They do both. As well as provide a description of the regulation's goals, context and examples. This is how regulation works. It typically starts with a rather vague law, then the regulatory agencies make up general rules to implement said law. Then they create a bunch of more detailed rules. Then as times change, they amend those rules. You can even ask them about novel situations and get a (non-binding) "opinion" from government agency. In my experience, the federal gov regulatory apparatus is not as inept as most people seem to think.