These attributes can show up in arbitrary API documentation (like Sequence.min()) because they're not underscored. As a result, people reading API documentation might encounter them, so we added information about them to the attributes reference.
They predate SE-0001, so that makes sense.
I don't think it makes sense to change how they're documented until something about their implementation changes; whether that means prefixing them with an underscore, adding them to Attr.def, or Swift Evolution-ing them to camel case.
@krilnon If these attributes are documented, it may give the impression that they are safe to use in third-party APIs. Could you at least add a disclaimer that they are currently for internal use only?
I can look into prefixing them with an underscore, if their originators @Douglas_Gregor and @jrose agree.