chomp $key; # don't care about trailing newline, if any.
foreach my $combine (keys %$self) {
  if (substr($key, 0, length $combine) eq $combine) {
    print "Found (prefix $combine): ", substr ($key, length $combine), "\n";
  }
  if (substr($key, -length $combine) eq $combine) {
    print "Found (suffix $combine): ",
      substr ($key, 0, length($key) - length $combine), "\n";
  }
}