In (info "(coreutils) join invocation") If the input has no unpairable lines, a GNU extension is available;
(shouldn't that ";" be ":"?)
the sort order can be any order that considers two fields to be equal if
and only if the sort comparison described above considers them to be
equal. For example:
$ cat file1...
OK, but perhaps in the previous paragraph give a mundane regular
example of join usage, instead of the first example be this special
exception.
