/usr/share/perl5/Mail/Message/Part.pm is in libmail-box-perl 2.117-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 | # Copyrights 2001-2014 by [Mark Overmeer].
#  For other contributors see ChangeLog.
# See the manual pages for details on the licensing terms.
# Pod stripped from pm file by OODoc 2.01.
use strict;
use warnings;
package Mail::Message::Part;
use vars '$VERSION';
$VERSION = '2.117';
use base 'Mail::Message';
use Scalar::Util    'weaken';
use Carp;
sub init($)
{   my ($self, $args) = @_;
    $args->{head} ||= Mail::Message::Head::Complete->new;
    $self->SUPER::init($args);
    confess "No container specified for part.\n"
        unless exists $args->{container};
    weaken($self->{MMP_container})
       if $self->{MMP_container} = $args->{container};
    $self;
}
sub coerce($@)
{   my ($class, $thing, $container) = (shift, shift, shift);
    if($thing->isa($class))
    {   $thing->container($container);
        return $thing;
    }
    return $class->buildFromBody($thing, $container, @_)
        if $thing->isa('Mail::Message::Body');
    # Although cloning is a Bad Thing(tm), we must avoid modifying
    # header fields of messages which reside in a folder.
    my $message = $thing->isa('Mail::Box::Message') ? $thing->clone : $thing;
    my $part    = $class->SUPER::coerce($message);
    $part->container($container);
    $part;
}
sub buildFromBody($$;@)
{   my ($class, $body, $container) = (shift, shift, shift);
    my @log  = $body->logSettings;
    my $head = Mail::Message::Head::Complete->new(@log);
    while(@_)
    {   if(ref $_[0]) {$head->add(shift)}
        else          {$head->add(shift, shift)}
    }
    my $part = $class->new
      ( head      => $head
      , container => $container
      , @log
      );
    $part->body($body);
    $part;
}
sub container(;$)
{   my $self = shift;
    return $self->{MMP_container} unless @_;
    $self->{MMP_container} = shift;
    weaken($self->{MMP_container});
}
sub toplevel()
{   my $body = shift->container or return;
    my $msg  = $body->message   or return;
    $msg->toplevel;
}
sub isPart() { 1 }
sub partNumber()
{   my $self = shift;
    my $body = $self->container or confess 'no container';
    $body->partNumberOf($self);
}
sub readFromParser($;$)
{   my ($self, $parser, $bodytype) = @_;
    my $head = $self->readHead($parser)
            || Mail::Message::Head::Complete->new
                 ( message     => $self
                 , field_type  => $self->{MM_field_type}
                 , $self->logSettings
                 );
    my $body = $self->readBody($parser, $head, $bodytype)
            || Mail::Message::Body::Lines->new(data => []);
    $self->head($head);
    $self->storeBody($body->contentInfoFrom($head));
    $self;
}
#-----------------
sub printEscapedFrom($)
{   my ($self, $out) = @_;
    $self->head->print($out);
    $self->body->printEscapedFrom($out);
}
sub destruct()
{  my $self = shift;
   $self->log(ERROR =>'You cannot destruct message parts, only whole messages');
   undef;
}
1;
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