Contraditions in users_guide/using-warnings.html
Lists are not updated in
E.g., it says "The warnings that are not enabled by -Wall are...-Wredundant-constraints", but then it says "This option is on by default". Also "-Worphans" is on none of the list of enabled or not enabled flags and also there is no mention in its description if its enabled by default or not. I guess there may be more.
Also, it may be worth mentioning that obsolete warnings or warnings subsumed by others are not on any of the list, or whatever the actual rule is.