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  if (App::Getconf->getopt->help) {
    print App::Getconf->help_message(
      screen   => 130,
      synopsis => "%0 [ options ] file ...",
    );
    exit 0;
  }

Supported options:

=over

=item C<screen> (default: 80)

Screen width, in columns.

=item C<arg0> (default: C<$0> with path stripped)

Name of the program. Usually C<$0> or a derivative.

=item C<synopsis> (default: C<%0 [ options ... ]>)

Short call summary. Any occurrence of C<%0> will be replaced with content of
C<arg0> option.

Synopsis may be also a multiline string or an array of single-line strings.

=item C<header>

=item C<description>

=item C<footer>

Three additional text fields: before synopsis, after synopsis but before
options list, after options list.

Text will be re-wrapped to fit on a terminal of C<screen> width. Empty lines
will be treated as paragraph separators, but single newline characters will
not be preserved.

Any occurrence of C<%0> will be replaced with content of C<arg0> option.

=item C<option_indent> (default: 2)

=item C<description_indent> (default: 6)

Indenting for option header ("--option" with parameter specification, if any)
and for option description.

=back

=cut

sub help_message {
  my ($self, %opts) = @_;

  $self = $static unless ref $self; # static call or non-static?

  $opts{screen}   ||= 80;
  $opts{arg0}     ||= (split m[/], $0)[-1];
  $opts{synopsis} ||= "%0 [ options ... ]";

  $opts{option_indent}      ||= 2;
  $opts{description_indent} ||= 6;

  # $opts{header}      ||= undef;
  # $opts{description} ||= undef;
  # $opts{footer}      ||= undef;

  my $help = "";
  my $line;
  my %format_markers;

  #---------------------------------------------------------
  # header {{{

  if ($opts{header}) {
    $line = _reformat($opts{header}, $opts{screen});
    $line =~ s/%0/$opts{arg0}/g;

    $help .= $line;
    $help .= "\n"; # additional empty line
  }

  # }}}
  #---------------------------------------------------------
  # synopsis {{{

  if (ref $opts{synopsis} eq 'ARRAY') {
    $line = join "\n", @{ $opts{synopsis} };
  } else {
    $line = $opts{synopsis};
  }
  $line =~ s/%0/$opts{arg0}/g;

  $line =~ s/\s+$//; # strip leading spaces

  if ($line =~ /\n./) {
    # multiline synopsis
    $format_markers{multiline_synopsis} = 1;

    $line =~ s/^[ \t]*/  /mg; # uniform indentation
    $help .= sprintf "Usage:\n%s\n", $line;

  } else {
    # single line synopsis

    $line =~ s/^\s+//; # strip leading spaces
    if (length($line) < $opts{screen} - 1 - length("Usage: ")) {
      $help .= sprintf "Usage: %s\n", $line;
    } else {
      $format_markers{multiline_synopsis} = 1;
      $help .= sprintf "Usage:\n%s\n", $line;
    }

  }

  # }}}
  #---------------------------------------------------------
  # description (below synopsis) {{{