# the shared-manager knows of \*STDIN, \*STDOUT, \*STDERR

   mce_open my $shared_in,  "<",  \*STDIN;   # ok
   mce_open my $shared_out, ">>", \*STDOUT;  # ok
   mce_open my $shared_err, ">>", \*STDERR;  # ok

   # but may not know of $non_shared_fh

   mce_open my $shared_fh, ">>", $non_shared_fh;