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  if (ref $param) {
    # it isn't a simple string, assume it is a filehandle
...
  } else {
    open $fh, "<", $param or die "$param: $!";
  }

  my $type = ref $param;
  if (!$type) {
...
  } elsif ($type eq 'IO::Handle') {
    # it's a non-overloaded IO::Handle
  } else { ... }

  if (!ref $param) {
    # scalar
...
  } elsif ($param->isa('IO::Handle')) {
    # is, or inherits from, IO::Handle
  } else { ... }

  if (!ref $param) {
    # scalar
  } elsif ($param->can('readline')) {
    # who knows what it is? But it supports a readline method ...
  } else { ... }

  Can't locate method 'readline' via package 'IO::StrangeHandle'