[ Summit: ]

Move to open. Related to conceptualization and should probably be tackled as part of that.

• The intention is not only to place a constraint on what types such as lock_guard may do with mutex types, but on what any code, including user code, may do with mutex types. Thus the constraints as they are apply to the mutex types themselves, not the current users of mutex types in the standard.
• This is a low priority issue; the wording as it is may be overly restrictive but this may not be a real issue.