Set#flatten_merge and Set#do_with_enum are called internally by other Set methods. Add nodoc comments to them so they don't show up in the list of undocumented things.
As far as Set#flatten_merge goes-- perhaps instead of marking it as :nodoc: it should be made private. This way it will also be ignored from docs.
That said-- perhaps the list of undocumented items should be updated to exclude private methods, which are currently already excluded from docs. If not, perhaps :nodoc: isn't the right answer and real docs should be added, since :nodoc: doesn't actually add any documentation here, so the change in doc coverage would just be superficial. Does anyone object to having docs for the internal methods? I wouldn't mind writing something.
Rdoc excluding private methods in its output but considering them undocumented sounds like an issue with rdoc. I'll take that up with Eric.
Set#flatten_merge needs to remain protected so that it can be called on other instances of Set. Take a look at Set#flatten for the example of that. I'm not sure it's useful outside that context which is why I favored marking it :nodoc: rather than adding actual documentation. That's just my opinion though, so feel free to document this function if you like.
This issue was solved with changeset r31527.
Pete, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
lib/set.rb (class Set): Add nodoc to internal-use methods. Patch by Pete Higgins. [Ruby 1.9 - Bug #4665]