On occasions when there are several commentators on a question or answer it can be useful to give a particular response to more than one of these, but SE only allows a response to be directed to a single person. I don't see why can't a message be shouldn't directed to multiple recipients. I think that this might involve a minor change to SE but save the users much time and effort.
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signs. – Alan Munn Jan 11 '19 at 22:02