This isn't very pretty, but first define a class:

package Undef;

sub AUTOLOAD {
  undef;
}
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and then you can string at the cost of a few parens with:

$text = ((
  $elt->first_child( 'subelt') || 'Undef'
  )->first_child( 'subsubelt')||'Undef'
  )->text();
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Don't like that? Well then you can just create a method to do the calls dynamically like this:

# Takes an array of anon arrays of method calls, and
# chains them.  Returns the first non-object of the end of
# the call.
sub chain_meth {
  my $obj = shift;
  my $last_call = pop;

  foreach my $call (@_) {
    my ($meth, @args) = @$call;
    $obj = $obj->$meth(@args);
    return $obj unless ref($obj);
  }

  # Make the last one respect context properly.
  my ($meth, @args) = @$last_call;
  return $obj->$meth(@args);
}
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and now you can:

$text = $elt->chain_meth(
  ["first_child", "subelt"], ["first_child", "subsubelt"], ["text"]
);
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